I changed jobs a couple of times in the middle of therapy and it was scary but I did it. You take the job and during the negotiation portion at the end you explain that you have a medical appointment on Thursday mornings so you won't be in until X o'clock and you'd be happy to stay late or come early some other morning, work lunch hour, etc. Just make it matter-of-fact and non-negotiable and if they want you, they will work around that. Lots of people have special circumstances that need working around and are doing "their" thing during work.

If you're free-lancing, you just say you're not free on Thursday morning, you have another "client" :-) Tell them you have another long-standing "job" Thursday mornings. I told the truth for my jobs, that I had therapy, got out the "I'm crazy, whether you like it or not so get use to it!" :-) bomb so everyone would know and be shocked that I dared speak of it. After I got to know everyone and they got to know me (my last job I worked at for 8-1/2 years) it got to be lots of fun even and extremely helpful to me in therapy (I got teased by one boss the "morning after" my appointments; apparently I was in a "bad" mood sometimes and I hadn't realized it or looked at it to see what had happened in the session the afternoon before to cause it).

But come up with a "story" you're comfortable with; doctor's appointment, other engagement, other job, whatever. It's your life and you can arrange it however it is comfortable for you! It's not slavery when you take a job, if the job is a good fit they'll let you work them in around your existing life.