Usually not a problem, my experience though is that you will be asked to move the appointment back an hour quite often. So you book a 1:00pm appointment for tomorrow this evening, when you call/text at 12:30pm tomorrow to confirm the date you might get asked if you can move the appointment to 2:00pm. (She may think you are a timewaster so won't have committed herself to the 1:00pm booking and wouldn't be ready to meet you at that time).