I leave my game going all night -- just like during the day when I'm not at home to play it. I had a problem with my first game(on "hard") before we'd gotten to farming -- the berry bush ran out, but I wasn't there to switch foragers to scientists, and the food ran out before I got enough tech to farm.
I set the replacement game to half speed until I got to farming -- they've been on normal speed all day with no problems.
I like leaving it on so those scientists collect tech points when I'm not looking
-- jen