Each section below has two boxes, the top runs on the main thread, the bottom on the compositor. The animations should be identical but start at different times.

This test is successful if the boxes are mostly in sync (there might be a small offset between them).

Start delay -30s (starts 30 seconds into animation by which the animation has finished, hence no animation)
Start delay -3s (starts 3 seconds into the animation, should finish first.)
Start delay 0s (no start delay, should finish second.)
Start delay 3s (starts 3 seconds after page load, should finish last.)