True, but it is common courtesy to not call in the dead of night, unless specified otherwise. The norm is up during the day, asleep at night, other schedules are the exception to the rule, and should be noted. If you are a buyer that has a flipped schedule, simply email rather than making the phone call.
As a buyer, I would never expect the seller to revolve around my schedule, rather I would work around his. Afterall, it's not like we go to the mall at 2am demanding they open the doors because we have a graveyard shift job and are not up during normal business hours.