The first six months I was seeing my therapists the times and days were really random. They really varied. They could 4 to 14 days in between, with most times being 6-10 days. We would just decide after the session, but sometimes she was really busy so she might email me after to change/or to give me the day.
After six months, she asked me if I wanted to come at the same time and day every week from then on. I was like YES. lol.
What I am trying to say, is that this is not so uncommon. You're a new client/patient so for now you are fitting in between. As you become more regular. Maybe let's say even 3-4 months and it seems like you want to continue long-term I think it would be very understanding to ask to come at same time/ same week.