The Mk2 does have a RTC onboard. We've not profiled how long it'll run without power, but the current guess is 7 days+ (it uses a 0.22F supercap). The unit doesn't have to be *on*, it just has to be either in the car (the mk2 takes a perm 12v feed as well as accessory) or plugged in at home to recharge the cap.

Resetting it from RDS time/DAB time/your PC's time is an option, yes.

Hugo