I was lucky enough to have an understanding boss, and I would come in late to the office every Thursday morning. He was an incredibly cranky and rude person otherwise, but it turned out he was on a prescription for Wellbutrin himself, so that made him more understanding. I did later ask my therapist what her other patients did, since she said she didn't do evening or weekend hours, but she didn't know how they got the time off.
Is it perhaps possible to say you're seeing a physical therapist instead? Maybe for an old injury?