That’s fine—the easiest thing is probably to finish out your current pack on schedule and start the next pack at the time you prefer. In that case you shouldn’t need any backup.
If you can’t wait for your next pack, just make sure you don’t allow more than 24 hours to pass between pills. So, for example, if you want to switch from morning to afternoon, you have to take 2 pills in one day—one at the old time and one at the new time. That’s probably better than waiting 36 hours and worrying about backup for a week! Only catch is you may also have to relabel your pill pack, because if you take the “Wednesday” pill on Tuesday night and forget to change the rest of the pack, confusion may abound.