That may not be useful to a lot of other people as a recommendation, but No Thank You, Evil! and Hero Kids are both designed with shorter scenarios and challenges in mind, due to their target audience. I don't think I've ever run NTYE! for more than an hour at a time. Outside specific games, I'd probably focus on lean games with simpler character sheets, like Risus or Fate Accelerated. FAE + It's Not My Fault would work well.
But… I mean… Almost all my weekly Roll20 gaming is comprised of 2 to 2.5 hour sessions, so… pretty much any system, I guess, if you're talking about being able to play multiple short sessions.
ALSO, any game where everyone playing is on the hook to come up with a lot of stuff out of their head, all the time, is probably best confined to shorter sessions. I find people lose their inventive steam after a few hours, so if you want to keep things popping in games where the players have to invent a lot of stuff on the fly, I'd recommend shorter sessions.