diff --git a/backend/internal/handler/grok_media.go b/backend/internal/handler/grok_media.go
index 8cd16924d..359b29e5b 100644
--- a/backend/internal/handler/grok_media.go
+++ b/backend/internal/handler/grok_media.go
@@ -188,6 +188,10 @@ func (h *OpenAIGatewayHandler) handleGrokMedia(c *gin.Context, endpoint service.
 	var oauth429FailoverState service.OpenAIOAuth429FailoverState
 	mediaEligibilityRejected := false
 	switchCount := 0
+	videoCreateStartedAt := ""
+	if isGrokVideoCreateEndpoint(endpoint) {
+		videoCreateStartedAt = service.GrokVideoPendingCreatedAtNow()
+	}
 	maxAccountSwitches := h.maxAccountSwitches
 	if maxAccountSwitches <= 0 {
 		maxAccountSwitches = 3
@@ -425,6 +429,8 @@ func (h *OpenAIGatewayHandler) handleGrokMedia(c *gin.Context, endpoint service.
 				VideoResolution:      result.VideoResolution,
 				VideoDurationSeconds: result.VideoDurationSeconds,
 				OriginalModel:        clientRequestedModel(c, requestModel),
+				// Wall-clock start for usage duration_ms: create accepted → first done discovery.
+				CreatedAt: videoCreateStartedAt,
 			}); err != nil {
 				reqLog.Warn("grok_media.store_video_pending_billing_failed",
 					zap.Int64("account_id", account.ID),
@@ -587,6 +593,14 @@ func prepareGrokVideoCompletionBilling(
 	merged.VideoResolution = service.NormalizeVideoBillingResolutionOrDefault(merged.VideoResolution)
 	// Official default duration is 8s when neither status nor create provided it.
 	merged.VideoDurationSeconds = service.NormalizeVideoBillingDurationSecondsOrDefault(merged.VideoDurationSeconds)
+	// E2E latency for async video: create accept → this discovery of done+url.
+	// Bill on discovery (status/content), not after further client polls; duration
+	// must not be only the single discovery hop (~hundreds of ms).
+	if pending != nil {
+		if e2e := service.GrokVideoE2EDuration(pending.CreatedAt, time.Now()); e2e > 0 {
+			merged.Duration = e2e
+		}
+	}
 	return &merged
 }
 
diff --git a/backend/internal/service/grok_media.go b/backend/internal/service/grok_media.go
index e0f6aa3d7..b2cf69c83 100644
--- a/backend/internal/service/grok_media.go
+++ b/backend/internal/service/grok_media.go
@@ -335,6 +335,43 @@ type GrokVideoPendingBilling struct {
 	VideoResolution      string `json:"video_resolution,omitempty"`
 	VideoDurationSeconds int    `json:"video_duration_seconds,omitempty"`
 	OriginalModel        string `json:"original_model,omitempty"`
+	// CreatedAt is when the gateway accepted the async create (RFC3339Nano UTC).
+	// duration_ms for deferred billing is measured from this instant until the
+	// first official done+video.url observation (status poll or content download),
+	// not the latency of that single discovery request alone.
+	CreatedAt string `json:"created_at,omitempty"`
+}
+
+// GrokVideoPendingCreatedAtNow formats a create-accept timestamp for pending billing.
+func GrokVideoPendingCreatedAtNow() string {
+	return time.Now().UTC().Format(time.RFC3339Nano)
+}
+
+// GrokVideoE2EDuration returns wall time from create accept to discovery of completion.
+// Returns 0 when CreatedAt is missing or unparseable (caller keeps poll-only Duration).
+func GrokVideoE2EDuration(createdAt string, discoveredAt time.Time) time.Duration {
+	createdAt = strings.TrimSpace(createdAt)
+	if createdAt == "" {
+		return 0
+	}
+	if discoveredAt.IsZero() {
+		discoveredAt = time.Now()
+	}
+	var created time.Time
+	var err error
+	if created, err = time.Parse(time.RFC3339Nano, createdAt); err != nil {
+		if created, err = time.Parse(time.RFC3339, createdAt); err != nil {
+			return 0
+		}
+	}
+	if created.IsZero() {
+		return 0
+	}
+	d := discoveredAt.Sub(created)
+	if d < 0 {
+		return 0
+	}
+	return d
 }
 
 func grokVideoPendingBillingKey(requestID string, userID, apiKeyID int64) string {
@@ -380,6 +417,12 @@ func (s *OpenAIGatewayService) StoreGrokVideoPendingBilling(
 	if pending.VideoDurationSeconds > 0 {
 		pending.VideoDurationSeconds = NormalizeVideoBillingDurationSecondsOrDefault(pending.VideoDurationSeconds)
 	}
+	// Always stamp create-accept time when missing so deferred duration_ms is E2E.
+	if strings.TrimSpace(pending.CreatedAt) == "" {
+		pending.CreatedAt = GrokVideoPendingCreatedAtNow()
+	} else {
+		pending.CreatedAt = strings.TrimSpace(pending.CreatedAt)
+	}
 	payload, err := json.Marshal(pending)
 	if err != nil {
 		return err
diff --git a/backend/internal/service/grok_media_video_billing_test.go b/backend/internal/service/grok_media_video_billing_test.go
index f3a3957bb..84dc2c107 100644
--- a/backend/internal/service/grok_media_video_billing_test.go
+++ b/backend/internal/service/grok_media_video_billing_test.go
@@ -2,10 +2,34 @@ package service
 
 import (
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 )
 
+func TestGrokVideoE2EDurationFromCreatedAt(t *testing.T) {
+	t.Parallel()
+	created := time.Now().UTC().Add(-45 * time.Second)
+	d := GrokVideoE2EDuration(created.Format(time.RFC3339Nano), time.Now().UTC())
+	require.GreaterOrEqual(t, d, 44*time.Second)
+	require.LessOrEqual(t, d, 47*time.Second)
+
+	require.Equal(t, time.Duration(0), GrokVideoE2EDuration("", time.Now()))
+	require.Equal(t, time.Duration(0), GrokVideoE2EDuration("not-a-time", time.Now()))
+	// Future CreatedAt clamps to zero (clock skew).
+	require.Equal(t, time.Duration(0), GrokVideoE2EDuration(time.Now().Add(time.Hour).UTC().Format(time.RFC3339Nano), time.Now()))
+}
+
+func TestGrokVideoPendingCreatedAtStampOnStoreShape(t *testing.T) {
+	t.Parallel()
+	// GrokVideoPendingCreatedAtNow must be parseable by GrokVideoE2EDuration.
+	stamp := GrokVideoPendingCreatedAtNow()
+	require.NotEmpty(t, stamp)
+	d := GrokVideoE2EDuration(stamp, time.Now().UTC().Add(2*time.Second))
+	require.GreaterOrEqual(t, d, time.Second)
+	require.LessOrEqual(t, d, 3*time.Second)
+}
+
 func TestIsGrokVideoStatusBillable(t *testing.T) {
 	t.Parallel()
 	// Official success: status=done + video.url