diff --git a/frontend/src/component/changeRequest/ChangeRequest/Changes/Change/MilestoneListRenderer.tsx b/frontend/src/component/changeRequest/ChangeRequest/Changes/Change/MilestoneListRenderer.tsx
index b2167f3b71..0ba98d7c46 100644
--- a/frontend/src/component/changeRequest/ChangeRequest/Changes/Change/MilestoneListRenderer.tsx
+++ b/frontend/src/component/changeRequest/ChangeRequest/Changes/Change/MilestoneListRenderer.tsx
@@ -70,6 +70,7 @@ const MilestoneListRendererCore = ({
                                         .intervalMinutes
                                 }
                                 targetMilestoneId={nextMilestoneId}
+                                sourceMilestoneStartedAt={milestone.startedAt}
                                 onSave={async (payload) => {
                                     await onUpdateAutomation(
                                         milestone.id,
diff --git a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/MilestoneProgressionForm/MilestoneProgressionForm.tsx b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/MilestoneProgressionForm/MilestoneProgressionForm.tsx
index 3e11b58f40..8f17fd52df 100644
--- a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/MilestoneProgressionForm/MilestoneProgressionForm.tsx
+++ b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/MilestoneProgressionForm/MilestoneProgressionForm.tsx
@@ -3,6 +3,7 @@ import BoltIcon from '@mui/icons-material/Bolt';
 import { useMilestoneProgressionForm } from '../hooks/useMilestoneProgressionForm.js';
 import { MilestoneProgressionTimeInput } from './MilestoneProgressionTimeInput.tsx';
 import type { ChangeMilestoneProgressionSchema } from 'openapi';
+import type { MilestoneStatus } from '../ReleasePlanMilestone/ReleasePlanMilestoneStatus.tsx';
 
 const StyledFormContainer = styled('div')(({ theme }) => ({
     display: 'flex',
@@ -49,12 +50,14 @@ const StyledButtonGroup = styled('div')(({ theme }) => ({
 const StyledErrorMessage = styled('span')(({ theme }) => ({
     color: theme.palette.error.main,
     fontSize: theme.typography.body2.fontSize,
-    marginRight: 'auto',
+    paddingLeft: theme.spacing(3.25),
 }));
 
 interface IMilestoneProgressionFormProps {
     sourceMilestoneId: string;
     targetMilestoneId: string;
+    sourceMilestoneStartedAt?: string | null;
+    status?: MilestoneStatus;
     onSubmit: (
         payload: ChangeMilestoneProgressionSchema,
     ) => Promise<{ shouldReset?: boolean }>;
@@ -64,12 +67,17 @@ interface IMilestoneProgressionFormProps {
 export const MilestoneProgressionForm = ({
     sourceMilestoneId,
     targetMilestoneId,
+    sourceMilestoneStartedAt,
+    status,
     onSubmit,
     onCancel,
 }: IMilestoneProgressionFormProps) => {
     const form = useMilestoneProgressionForm(
         sourceMilestoneId,
         targetMilestoneId,
+        {},
+        sourceMilestoneStartedAt,
+        status,
     );
 
     const handleSubmit = async () => {
@@ -102,10 +110,10 @@ export const MilestoneProgressionForm = ({
                     onTimeUnitChange={form.handleTimeUnitChange}
                 />
             </StyledTopRow>
+            {form.errors.time && (
+                <StyledErrorMessage>{form.errors.time}</StyledErrorMessage>
+            )}
             <StyledButtonGroup>
-                {form.errors.time && (
-                    <StyledErrorMessage>{form.errors.time}</StyledErrorMessage>
-                )}
                 <Button variant='outlined' onClick={onCancel} size='small'>
                     Cancel
                 </Button>
diff --git a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestone/MilestoneNextStartTime.tsx b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestone/MilestoneNextStartTime.tsx
index 9beaf268fd..fe405bb91b 100644
--- a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestone/MilestoneNextStartTime.tsx
+++ b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestone/MilestoneNextStartTime.tsx
@@ -1,12 +1,12 @@
 import { styled } from '@mui/material';
 import HourglassEmptyOutlinedIcon from '@mui/icons-material/HourglassEmptyOutlined';
 import type { IReleasePlanMilestone } from 'interfaces/releasePlans';
-import { formatDateYMDHMS } from 'utils/formatDate';
+import { formatDateYMDHM } from 'utils/formatDate';
 import { isToday, isTomorrow, format } from 'date-fns';
 import { calculateMilestoneStartTime } from '../utils/calculateMilestoneStartTime.ts';
 import { useUiFlag } from 'hooks/useUiFlag';
 
-const formatSmartDate = (date: Date): string => {
+export const formatSmartDate = (date: Date): string => {
     const timeString = format(date, 'HH:mm');
 
     if (isToday(date)) {
@@ -17,7 +17,7 @@ const formatSmartDate = (date: Date): string => {
     }
 
     // For other dates, show full date with time
-    return formatDateYMDHMS(date);
+    return formatDateYMDHM(date);
 };
 
 const StyledTimeContainer = styled('span')(({ theme }) => ({
@@ -74,7 +74,7 @@ export const MilestoneNextStartTime = ({
     );
 
     const text = projectedStartTime
-        ? `Starting ${formatSmartDate(projectedStartTime)}`
+        ? `Starting after ${formatSmartDate(projectedStartTime)}`
         : 'Waiting to start';
 
     return (
diff --git a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestone/MilestoneTransitionDisplay.tsx b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestone/MilestoneTransitionDisplay.tsx
index 2afed24fdc..1bfe825e50 100644
--- a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestone/MilestoneTransitionDisplay.tsx
+++ b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestone/MilestoneTransitionDisplay.tsx
@@ -90,9 +90,16 @@ const StyledButtonGroup = styled('div', {
     }),
 }));
 
+const StyledErrorMessage = styled('span')(({ theme }) => ({
+    color: theme.palette.error.main,
+    fontSize: theme.typography.body2.fontSize,
+    paddingLeft: theme.spacing(3.25),
+}));
+
 interface IMilestoneTransitionDisplayProps {
     intervalMinutes: number;
     targetMilestoneId: string;
+    sourceMilestoneStartedAt?: string | null;
     onSave: (
         payload: ChangeMilestoneProgressionSchema,
     ) => Promise<{ shouldReset?: boolean }>;
@@ -105,6 +112,7 @@ interface IMilestoneTransitionDisplayProps {
 export const MilestoneTransitionDisplay = ({
     intervalMinutes,
     targetMilestoneId,
+    sourceMilestoneStartedAt,
     onSave,
     onDelete,
     milestoneName,
@@ -119,6 +127,8 @@ export const MilestoneTransitionDisplay = ({
             timeValue: initial.value,
             timeUnit: initial.unit,
         },
+        sourceMilestoneStartedAt,
+        status,
     );
 
     const currentIntervalMinutes = form.getIntervalMinutes();
@@ -130,9 +140,19 @@ export const MilestoneTransitionDisplay = ({
         form.setTimeUnit(newInitial.unit);
     }, [intervalMinutes]);
 
+    useEffect(() => {
+        if (!hasChanged) {
+            form.clearErrors();
+        }
+    }, [hasChanged, form.clearErrors]);
+
     const handleSave = async () => {
         if (!hasChanged) return;
 
+        if (!form.validate()) {
+            return;
+        }
+
         const payload: ChangeMilestoneProgressionSchema = {
             targetMilestone: targetMilestoneId,
             transitionCondition: {
@@ -151,6 +171,7 @@ export const MilestoneTransitionDisplay = ({
         const initial = getTimeValueAndUnitFromMinutes(intervalMinutes);
         form.setTimeValue(initial.value);
         form.setTimeUnit(initial.unit);
+        form.clearErrors();
     };
 
     const handleKeyDown = (event: React.KeyboardEvent) => {
@@ -192,6 +213,9 @@ export const MilestoneTransitionDisplay = ({
                     </StyledButtonGroup>
                 )}
             </StyledDisplayContainer>
+            {form.errors.time && (
+                <StyledErrorMessage>{form.errors.time}</StyledErrorMessage>
+            )}
             {hasChanged && (
                 <StyledButtonGroup hasChanged={true}>
                     <Button
diff --git a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestoneItem/MilestoneAutomation.tsx b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestoneItem/MilestoneAutomation.tsx
index 0da49b965c..7d9b6d4580 100644
--- a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestoneItem/MilestoneAutomation.tsx
+++ b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/ReleasePlanMilestoneItem/MilestoneAutomation.tsx
@@ -93,6 +93,8 @@ export const MilestoneAutomation = ({
                 <MilestoneProgressionForm
                     sourceMilestoneId={milestone.id}
                     targetMilestoneId={nextMilestoneId}
+                    sourceMilestoneStartedAt={milestone.startedAt}
+                    status={status}
                     onSubmit={onChangeProgression}
                     onCancel={onCloseProgressionForm}
                 />
@@ -102,6 +104,7 @@ export const MilestoneAutomation = ({
                         effectiveTransitionCondition.intervalMinutes
                     }
                     targetMilestoneId={nextMilestoneId}
+                    sourceMilestoneStartedAt={milestone.startedAt}
                     onSave={onChangeProgression}
                     onDelete={() => onDeleteProgression(milestone)}
                     milestoneName={milestone.name}
diff --git a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/hooks/useMilestoneProgressionForm.ts b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/hooks/useMilestoneProgressionForm.ts
index 654003b9bb..78729f1290 100644
--- a/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/hooks/useMilestoneProgressionForm.ts
+++ b/frontend/src/component/feature/FeatureView/FeatureOverview/ReleasePlan/hooks/useMilestoneProgressionForm.ts
@@ -1,4 +1,7 @@
-import { useState } from 'react';
+import { useState, useCallback } from 'react';
+import { isPast, addMinutes } from 'date-fns';
+import { formatSmartDate } from '../ReleasePlanMilestone/MilestoneNextStartTime.tsx';
+import type { MilestoneStatus } from '../ReleasePlanMilestone/ReleasePlanMilestoneStatus.tsx';
 
 const MAX_INTERVAL_MINUTES = 525600; // 365 days
 
@@ -42,6 +45,8 @@ export const useMilestoneProgressionForm = (
         timeUnit: initialTimeUnit = 'hours',
         timeValue: initialTimeValue = 5,
     }: MilestoneProgressionFormDefaults = {},
+    sourceMilestoneStartedAt?: string | null,
+    status?: MilestoneStatus,
 ) => {
     const [timeUnit, setTimeUnit] = useState<TimeUnit>(initialTimeUnit);
     const [timeValue, setTimeValue] = useState(initialTimeValue);
@@ -78,6 +83,22 @@ export const useMilestoneProgressionForm = (
             newErrors.time = 'Time interval cannot exceed 365 days';
         }
 
+        // Only validate against current time for active/paused milestones
+        // Completed and not-started milestones shouldn't validate against current time
+        if (
+            sourceMilestoneStartedAt &&
+            total > 0 &&
+            (status === 'active' || status === 'paused')
+        ) {
+            const startDate = new Date(sourceMilestoneStartedAt);
+            const nextMilestoneDate = addMinutes(startDate, total);
+
+            if (isPast(nextMilestoneDate)) {
+                const formattedDate = formatSmartDate(nextMilestoneDate);
+                newErrors.time = `Next milestone can't start in the past (${formattedDate})`;
+            }
+        }
+
         setErrors(newErrors);
         return Object.keys(newErrors).length === 0;
     };
@@ -96,12 +117,17 @@ export const useMilestoneProgressionForm = (
         }
     };
 
+    const clearErrors = useCallback(() => {
+        setErrors({});
+    }, []);
+
     return {
         timeUnit,
         setTimeUnit,
         timeValue,
         setTimeValue,
         errors,
+        clearErrors,
         validate,
         getProgressionPayload,
         getIntervalMinutes,