I just spent weeks worrying about my snake because it wouldn't go poo. Sometimes it takes a while, especially if they haven't been eating too frequently. Gently feel your snake's underside from about halfway down all the way to the tail. If you feel some semi-hard material (it will feel like poop) near the tail it may be very soon. If you just feel good size softer material further up near the stomach it may be a little while.

Good luck!