diff --git a/dom/animation/Animation.h b/dom/animation/Animation.h
index ae168c52127d..7e946b2f124d 100644
--- a/dom/animation/Animation.h
+++ b/dom/animation/Animation.h
@@ -486,6 +486,41 @@ protected:
     return GetCurrentTimeForHoldTime(Nullable<TimeDuration>());
   }
 
+  // Earlier side of the elapsed time range reported in CSS Animations and CSS
+  // Transitions events.
+  //
+  // https://drafts.csswg.org/css-animations-2/#interval-start
+  // https://drafts.csswg.org/css-transitions-2/#interval-start
+  StickyTimeDuration
+  IntervalStartTime(const StickyTimeDuration& aActiveDuration) const
+  {
+    MOZ_ASSERT(AsCSSTransition() || AsCSSAnimation(),
+               "Should be called for CSS animations or transitions");
+    static constexpr StickyTimeDuration zeroDuration = StickyTimeDuration();
+    return std::max(
+      std::min(StickyTimeDuration(-mEffect->SpecifiedTiming().Delay()),
+               aActiveDuration),
+      zeroDuration);
+  }
+
+  // Later side of the elapsed time range reported in CSS Animations and CSS
+  // Transitions events.
+  //
+  // https://drafts.csswg.org/css-animations-2/#interval-end
+  // https://drafts.csswg.org/css-transitions-2/#interval-end
+  StickyTimeDuration
+  IntervalEndTime(const StickyTimeDuration& aActiveDuration) const
+  {
+    MOZ_ASSERT(AsCSSTransition() || AsCSSAnimation(),
+               "Should be called for CSS animations or transitions");
+
+    static constexpr StickyTimeDuration zeroDuration = StickyTimeDuration();
+    return std::max(
+      std::min((EffectEnd() - mEffect->SpecifiedTiming().Delay()),
+               aActiveDuration),
+      zeroDuration);
+  }
+
   nsIDocument* GetRenderedDocument() const;
 
   RefPtr<AnimationTimeline> mTimeline;
diff --git a/layout/style/nsAnimationManager.cpp b/layout/style/nsAnimationManager.cpp
index 1f541c3b6923..521a12cfa426 100755
--- a/layout/style/nsAnimationManager.cpp
+++ b/layout/style/nsAnimationManager.cpp
@@ -193,7 +193,6 @@ CSSAnimation::QueueEvents(const StickyTimeDuration& aActiveTime)
     return;
   }
 
-  static constexpr StickyTimeDuration zeroDuration = StickyTimeDuration();
   uint64_t currentIteration = 0;
   ComputedTiming::AnimationPhase currentPhase;
   StickyTimeDuration intervalStartTime;
@@ -211,14 +210,8 @@ CSSAnimation::QueueEvents(const StickyTimeDuration& aActiveTime)
         currentIteration == mPreviousIteration) {
       return;
     }
-    intervalStartTime =
-      std::max(std::min(StickyTimeDuration(-mEffect->SpecifiedTiming().Delay()),
-                        computedTiming.mActiveDuration),
-               zeroDuration);
-    intervalEndTime =
-      std::max(std::min((EffectEnd() - mEffect->SpecifiedTiming().Delay()),
-                        computedTiming.mActiveDuration),
-               zeroDuration);
+    intervalStartTime = IntervalStartTime(computedTiming.mActiveDuration);
+    intervalEndTime = IntervalEndTime(computedTiming.mActiveDuration);
 
     uint64_t iterationBoundary = mPreviousIteration > currentIteration
                                  ? currentIteration + 1
diff --git a/layout/style/nsTransitionManager.cpp b/layout/style/nsTransitionManager.cpp
index 5ccbc35c2a55..9f8fa3338d56 100755
--- a/layout/style/nsTransitionManager.cpp
+++ b/layout/style/nsTransitionManager.cpp
@@ -206,12 +206,8 @@ CSSTransition::QueueEvents(const StickyTimeDuration& aActiveTime)
     ComputedTiming computedTiming = mEffect->GetComputedTiming();
 
     currentPhase = static_cast<TransitionPhase>(computedTiming.mPhase);
-    intervalStartTime =
-      std::max(std::min(StickyTimeDuration(-mEffect->SpecifiedTiming().Delay()),
-                        computedTiming.mActiveDuration), zeroDuration);
-    intervalEndTime =
-      std::max(std::min((EffectEnd() - mEffect->SpecifiedTiming().Delay()),
-                        computedTiming.mActiveDuration), zeroDuration);
+    intervalStartTime = IntervalStartTime(computedTiming.mActiveDuration);
+    intervalEndTime = IntervalEndTime(computedTiming.mActiveDuration);
   }
 
   // TimeStamps to use for ordering the events when they are dispatched. We