You could always get an old graflex solenoid and hook it up to a few batteries on a wire, or even to a small RC transceiver? They also have screw in self timers that you can use for large format.
I actually scored a graflex solenoid so i'm going to give it a shot. As I said in my original post, I have zero interest in those screw in timers. I had one, it lasted 10 minutes and isn't any where close to what I need.