My current one is at a small private practice, but she does her own scheduling. I can generally come at the same time and day, but we only book out a couple appointments at a time. Sometimes, like this week, she'll be unavailable (going out of town for a conference, etc.) on my normal day, so I switched to a different day when she's back in town. I've also scheduled a couple extra sessions last minute, because I had been trying to do every other week due to finances, but have realized I need more support than that. Even though it kinda stresses me out to not always have "my" time slot, she's usually pretty flexible in that I've been able to schedule extra support sessions on short notice (like 2 days notice) with several options available.

Previous Ts have usually always had the same day & time slot open for me, barring extenuating circumstances.