There should be! When you start a non-scenario game with bots, just set the Timer setting to the amount you want.
My apologies! I misinterpreted your question. I agree! There should be a time limit option in singleplayer, for now you can just use Pass and Play with bots and skip the turn of the second human player manually, but it's not a perfect solution.
I hope so! I've suggested it on the Discord as well to get it some extra exposure :D