I'm guessing often users are cheating with delays to make triggers play one after another (I do)
They would calculate the total time for the first trigger, then start by adding the same delay to the second.
In Apple's Keynote app, an event is played WITH the one before by default, but you can also set it to play AFTER and you can even add a delay.
I find this system very effective. Without going for a full timeline edit, it allows for just the complexity you need for prototyping and, I think, web anims. It's also easy to read it, facilitating the future maintenance.