I haven't seen any 12V timers around as yet. But that would be the way to go. What I DO have lying around, now that I remember, is a clothes dryer control timer - although it handles 240v, it's basically a mechanical, spring driven timer with a big dial knob that you turn to however many minutes you want to run (up to 3 hours, I think), and then it just ticks away and runs down. I could just mount that under my scope board with a pulley belt around the timer knob - forget about connecting it to any power at all! The timer does about 270 degrees rotation when fully wound, and does this in 3 hours. All I need to do is make the pulley wheel the correct size to make the dobson base turn once in 24 hours. A clockwork tracking motor - now THAT'S old skool hehe!
Cheers, Graham