Maybe I'm misunderstanding the question, but I don't see why the timer wouldn't be good next year, assuming they are stored indoors.
If your timers were plug in types, then there should be no issue. If they were battery operated, remove the batteries before storing them as if they do go dead they could possibly leak.
These are digital timers with sealed rechargable batteries. I worry that if I unplug them and store them away the batteries will discharge, and not recharge, when I need them next December.
I think I didn't provide enough information in my initial post. These timers are digital and have rechargable batteries inside the unit.
Then there is nothing to worry about. The batteries will go dead perhaps, but once they are plugged in should recharge next year.