I have a regular time slot, which used to be every week, but then we moved to every other week. Lately, I've needed to go back to weekly, so my every other week slot is pre-set, but for the off week, I have to take whatever time T might have available. She's usually able to give me a time that will work with my schedule.

I like the consistency of knowing when my appointment will be week after week. It removes a source of anxiety, as changing schedules tend to make me anxious.