my guess is (and only my guess...as i don't have a pro studio)....that a very liberal 9-5 hours would be set to encourage use of business hours, but that most studios in markets other than huge ones like LA or Nashville, would be happy to stretch the hours and weekends for just about anyone who asks.....
think of it from a customer point of view......i work....if they couldn't do it on the weekend would i take off work or find another place that would do it on the weekend.......i'd find another place.......would i tell others about how they wouldn't do it....probably............my opinion would be that if you're in a mid/small sized market, and unless you are the local leading studio, try to do what they want when they want