Presumably you’d all be fine with OP saying she has medical treatment twice a week, or physio therapy. nobody has said the OP shouldn’t have a hobby so stop being so obtuse.
With medical treatment you are generally at the mercy of the medical profession to arrange those treatments within their appointment schedules, and so it stands to reason that sometimes those appointments will fall in work hours.
As it happens I have a lot of medical appointments, and some of those are flexible which I arrange to fit around my work hours, and more often than not I use my annual leave to accommodate other medical appointments. But not everyone is always able to do that.
But a hobby is by definition a hobby, a relaxation, something you enjoy doing, and that is something that you have control over.
Put it into perspective, there are 24 hours in a day, that’s 168 hours a week. Take out 40 hours for 8 hours of sleep a day and you’re left with 128 hours. Take off twenty hours for potential work and you’re left with 108 hours. And you honestly think that this hobby can only be fitted into a couple of hours during the explicit 20 hours that OP could be working and not into some of the remaining 108 hours? Get real.
Of course OP should do her hobby. But you work your hobbies around your life, especially when it comes to having to work, not the other way around.
How many posts do we see on here about deadbeat men who do their hobbies every weekend because they don’t want to look after the kids. Presumably you’d say it was ok to opt out of family life to do their hobby if that was done in the name of mental illness, in the same way the OP and others are opting out of work?
Edited to correct the hours calculation, which actually means that the OP has considerably more hours to do her hobby.