Well, I think I separated beat loops out into their own instrument tracks and mixed everything as much as I can for one night. Bloody annoying detail work most of the time, until you step back far enough to listen to the mix with fresh ears and hear things moving along nicely. Trouble sets in when you realize your ears really aren't all that fresh after a couple of hours, and you're just tweaking small bits without making significant improvements. Then it's time to stop.
Especially if you need to do lame things like "get to bed at a reasonable hour and not be going over and over the track in your mind having random inspirations that you just have to get up and try out, keeping yourself up another fifteen minutes or a half hour on a work night." ;-)