It’s all good. That’s what I did. Didn’t drain battery and (I think), the radio has a cut off after a while so it doesn’t kill the battery. Although I haven’t left my radio on for that long to find out.
I left mine on with the door locked and it was fine. Couldn’t be bothered to wait around in the car doing nothing for an hour, especially for the reason that I didn’t know if it was going to work after that time. When I returned it must have been something like 58 or 59 minutes as at first it still said “SAFE”, then all of a sudden it was ready to have the code put in again.
An hour is a very long time when you have nothing to do and are watching the clock!