I think it's reasonable to ask, but you have to be prepared and willing to accept a no. Your T is a person too with his own needs. He may need this "break" from work related things to truly give his best to his clients including you. If he can't email on the weekends, maybe there are other workarounds. Some have already been suggested. Could you possibly change your appointment day to later in the week so the topics are fresh in your mind?