diff --git a/packages/destination-actions/src/destinations/snap-conversions-api/_tests_/index.test.ts b/packages/destination-actions/src/destinations/snap-conversions-api/_tests_/index.test.ts
index fd49b81b6d5..a5fce9329e1 100644
--- a/packages/destination-actions/src/destinations/snap-conversions-api/_tests_/index.test.ts
+++ b/packages/destination-actions/src/destinations/snap-conversions-api/_tests_/index.test.ts
@@ -2,6 +2,7 @@ import nock from 'nock'
 import { createTestEvent, createTestIntegration } from '@segment/actions-core'
 import Definition from '../index'
 import { smartHash } from '../reportConversionEvent/utils'
+import { FLAGON_EVENT_TIME_IN_SECONDS } from '../reportConversionEvent/snap-capi-v3'
 
 const testDestination = createTestIntegration(Definition)
 
@@ -838,4 +839,56 @@ describe('Snap Conversions API ', () => {
       expect(user_data.sc_cookie1).toEqual((testEvent.integrations?.['Snap Conversions Api'] as any)?.uuid_c1)
     })
   })
+
+  describe('event_time normalization (snap-capi-event-time-in-seconds flag)', () => {
+    const FLAG = FLAGON_EVENT_TIME_IN_SECONDS
+
+    it('emits milliseconds (13 digits) when the flag is OFF (default, unchanged behavior)', async () => {
+      const { data } = await reportConversionEvent({
+        mapping: { event_type: 'PURCHASE', event_conversion_type: 'WEB' }
+      })
+
+      // Date.parse('2022-05-12T15:21:15.449Z') === 1652368875449 (milliseconds)
+      expect(data.event_time).toEqual(1652368875449)
+    })
+
+    it('converts an ISO8601 timestamp to Unix seconds (10 digits) when the flag is ON', async () => {
+      const { data } = await reportConversionEvent({
+        features: { [FLAG]: true },
+        mapping: { event_type: 'PURCHASE', event_conversion_type: 'WEB' }
+      })
+
+      // 1652368875449 ms -> 1652368875 s
+      expect(data.event_time).toEqual(1652368875)
+    })
+
+    it('reproduces STRATCONN-6951: offline lead ms timestamp becomes valid seconds when ON', async () => {
+      const { data } = await reportConversionEvent({
+        event: { ...testEvent, timestamp: '2026-05-20T19:29:22.702Z' },
+        features: { [FLAG]: true },
+        mapping: { event_name: 'SIGN_UP', event_conversion_type: 'OFFLINE' }
+      })
+
+      // 1779305362702 ms (rejected by Snap as invalid) -> 1779305362 s (valid)
+      expect(data.event_time).toEqual(1779305362)
+    })
+
+    it('divides a numeric millisecond event_time (13 digits) to seconds when ON', async () => {
+      const { data } = await reportConversionEvent({
+        features: { [FLAG]: true },
+        mapping: { event_type: 'PURCHASE', event_conversion_type: 'WEB', event_time: '1652368875449' }
+      })
+
+      expect(data.event_time).toEqual(1652368875)
+    })
+
+    it('leaves a numeric second event_time (10 digits) untouched when ON', async () => {
+      const { data } = await reportConversionEvent({
+        features: { [FLAG]: true },
+        mapping: { event_type: 'PURCHASE', event_conversion_type: 'WEB', event_time: '1652368875' }
+      })
+
+      expect(data.event_time).toEqual(1652368875)
+    })
+  })
 })
diff --git a/packages/destination-actions/src/destinations/snap-conversions-api/reportConversionEvent/snap-capi-v3.ts b/packages/destination-actions/src/destinations/snap-conversions-api/reportConversionEvent/snap-capi-v3.ts
index 48cfc322b78..c8d8dea1a6d 100644
--- a/packages/destination-actions/src/destinations/snap-conversions-api/reportConversionEvent/snap-capi-v3.ts
+++ b/packages/destination-actions/src/destinations/snap-conversions-api/reportConversionEvent/snap-capi-v3.ts
@@ -1,4 +1,4 @@
-import { ExecuteInput, ModifiedResponse, RequestClient } from '@segment/actions-core'
+import { ExecuteInput, Features, ModifiedResponse, RequestClient } from '@segment/actions-core'
 import { Payload } from './generated-types'
 import { Settings } from '../generated-types'
 import {
@@ -11,11 +11,17 @@ import {
   emptyStringToUndefined,
   parseNumberSafe,
   parseDateSafe,
+  normalizeToUnixSeconds,
   smartHash
 } from './utils'
 import { processHashing } from '../../../lib/hashing-utils'
 import { SNAP_CONVERSIONS_API_VERSION } from '../versioning-info'
 
+// When enabled, `event_time` is normalized to a Unix timestamp in seconds (10 digits) as
+// required by Snap's Conversions API, instead of the milliseconds (13 digits) produced by
+// `Date.parse`. Gated for safe rollout on this high-volume destination.
+export const FLAGON_EVENT_TIME_IN_SECONDS = 'snap-capi-event-time-in-seconds'
+
 const CURRENCY_ISO_4217_CODES = new Set([
   'USD',
   'AED',
@@ -607,7 +613,7 @@ const getSupportedActionSource = (action_source: string | undefined): string | u
     : undefined
 }
 
-const buildPayloadData = (payload: Payload, settings: Settings) => {
+const buildPayloadData = (payload: Payload, settings: Settings, features?: Features) => {
   // event_conversion_type is a required parameter whose value is enforced as
   // always OFFLINE, WEB, or MOBILE_APP, so in practice action_source will always have a value.
   const action_source =
@@ -624,7 +630,13 @@ const buildPayloadData = (payload: Payload, settings: Settings) => {
   // Handle the case where a number is passed instead of an ISO8601 timestamp
   const event_time_number = parseNumberSafe(payload_event_time ?? '')
   const event_time_date_time = parseDateSafe(payload_event_time ?? '')
-  const event_time = event_time_date_time ?? event_time_number
+  const event_time_raw = event_time_date_time ?? event_time_number
+  // Snap's Conversions API expects `event_time` in seconds. `Date.parse` yields milliseconds,
+  // which Snap rejects as an invalid Unix timestamp. Normalize to seconds when the flag is on.
+  const event_time =
+    features?.[FLAGON_EVENT_TIME_IN_SECONDS] && event_time_raw != null
+      ? normalizeToUnixSeconds(event_time_raw)
+      : event_time_raw
 
   const app_data = action_source === 'app' ? buildAppData(payload, settings) : undefined
   const user_data = buildUserData(payload)
@@ -733,9 +745,9 @@ export const performSnapCAPIv3 = async (
   request: RequestClient,
   data: ExecuteInput<Settings, Payload>
 ): Promise<ModifiedResponse<unknown>> => {
-  const { payload, settings } = data
+  const { payload, settings, features } = data
 
-  const payloadData = buildPayloadData(payload, settings)
+  const payloadData = buildPayloadData(payload, settings, features)
 
   validatePayload(payloadData)
   validateSettingsConfig(settings, payloadData.action_source)
diff --git a/packages/destination-actions/src/destinations/snap-conversions-api/reportConversionEvent/utils.ts b/packages/destination-actions/src/destinations/snap-conversions-api/reportConversionEvent/utils.ts
index 4a48acce3e5..dbdb44ab85f 100644
--- a/packages/destination-actions/src/destinations/snap-conversions-api/reportConversionEvent/utils.ts
+++ b/packages/destination-actions/src/destinations/snap-conversions-api/reportConversionEvent/utils.ts
@@ -70,6 +70,20 @@ export const parseDateSafe = (v: string | undefined): number | undefined => {
   return Number.isSafeInteger(parsed) ? parsed : undefined
 }
 
+// Snap's Conversions API expects `event_time` as a Unix timestamp in seconds (e.g. 1777819609).
+// `Date.parse` (and some upstream sources) produce milliseconds (e.g. 1777819609520), which Snap's
+// offline endpoint interprets as seconds far in the future and rejects with
+// "Param data['event_time'] is an invalid Unix timestamp." Normalize milliseconds to seconds
+// while leaving values already in seconds untouched.
+//
+// Any value >= 1e12 is treated as milliseconds: 1e12 ms is 2001-09-09, whereas a seconds
+// timestamp does not reach 1e12 until the year 33658 — so modern seconds and milliseconds
+// timestamps never overlap this threshold.
+const MILLISECONDS_THRESHOLD = 1e12
+
+export const normalizeToUnixSeconds = (timestamp: number): number =>
+  timestamp >= MILLISECONDS_THRESHOLD ? Math.floor(timestamp / 1000) : Math.floor(timestamp)
+
 export const smartHash = (
   value: string | undefined,
   cleaningFunction?: (value: string) => string