http://www.twitch.tv/dominatedominion/b/333131696

3:48:20 ish and on. Pay attention to Swain's death and revive timer. Notice when Le Blanc dies, Swain has 6 seconds left on his timer and Leblanc doesn't catch the revive wave. Then pay attention to when Jax dies, Le Blanc has 8 seconds left on her timer and Jax catches the revive wave (spawns 3 seconds later).

Is it correct, then, that the revive wave mechanic has a cut off between 8 and 6 seconds left on the team's revive? Or is it more complex/involved than that? Can a Riot person clarify please?

This definitely seems bizarre. In that same fight when Warwick and Riven die within a few seconds of each other, they get put on the same wave, but it doesn't make sense for the Leblanc/Jax case.

I don't see where is the confusion. So I will say this, once someone dies, he opens a 12 seconds window (or 13 according to my testing) if someone dies in those 13 seconds, he goes into window, otherwise it doesnt.
Swain was already dead for more than 13 seconds by the time leblanc died. Yet leblanc was only dead for around 13 seconds, the time jax died.

The wave revive is set by the game timer, not time from each death.

I think each wave interval was like 15 seconds or so.