Start sooner rather than later. If you're not sure if it's today or tomorrow, you are much safer starting today.

It's easy to tell though: what day of the week did you start the sugar pills on? That's the day of the week you'll start the new pack on

I agree; its much better and safer to start it sooner rather than later. You can change the time you take the pill, but only if you are changing it to an earlier time (for example, if it used to be 10 pm you can start taking it at 9 am 1 pm 5 pm...any time earlier with no problems). If you are changing it to a later time, it is okay if it is within a few hours, but if its any more than 6 hours you will be less protected. If you want to stay safe when changing to a later pill, take two pills in one day (your first pill at the normal time you were taking your pills at, and your second pill at the new time). Then the next days keep taking it at the new time.