--- a/dom/animation/AnimationEffectTiming.cpp
+++ b/dom/animation/AnimationEffectTiming.cpp
@@ -26,17 +26,23 @@ PostSpecifiedTimingUpdated(KeyframeEffec
   if (aEffect) {
     aEffect->NotifySpecifiedTimingUpdated();
   }
 }
 
 void
 AnimationEffectTiming::SetDelay(double aDelay)
 {
-  // TODO: Bug 1244633 - implement AnimationEffectTiming delay
+  TimeDuration delay = TimeDuration::FromMilliseconds(aDelay);
+  if (mTiming.mDelay == delay) {
+    return;
+  }
+  mTiming.mDelay = delay;
+
+  PostSpecifiedTimingUpdated(mEffect);
 }
 
 void
 AnimationEffectTiming::SetEndDelay(double aEndDelay)
 {
   TimeDuration endDelay = TimeDuration::FromMilliseconds(aEndDelay);
   if (mTiming.mEndDelay == endDelay) {
     return;