If the customer has a controller with thier pool equipment, aqualink, jandy, compool most of the better controllers have freeze protection circuits. If the pump runs at night in freeze protection and then runs its regular schedule during the day and it's cold, they could get a whopper utility bill.
Try rescheduling the pump controller to turn on at 2am when it's cold and have it run until 6 am. that way it doesn't run twice. If they are on TOu metering, even better.