Timeouts in casual games

Today, as I went to make my moves in casual Games that I had going on, I noticed that I was no longer in one of the games. At first I thought it could be I somehow mistakenly left the game instead of returning to lobby after last tur. However, I also noticed a LOT of the players had left the other games I was in, due to timeout.

Haven't had that before, thought I'd post about this here.

I can't figure out how this works. in one game, one player went inactive for five turns without timing out, another player timed out the first inactive turn. how does this work?