It's a bummer when you're working on a project and your development time is limited. I find myself in that position a lot lately, and one of the best remedies I have is to keep my mind focused, even when I can't actually spend time working.
I usually pick a problem I'm working on and spend time thinking about it while I'm doing other mindless tasks, like cleaning the dishes or taking out the trash. If I have time, making sketches of things can also help.
That way, when I get back to my dev machine, I'm ready to get to work again - rather than spending a bunch of time reorienting myself.