Christ on a bike. Please tell me this is a joke. If not, YABEU.
As umpteen people have reiterated, teachers do not, by any stretch of the imagination, work short days. And your son's teacher hasn't just been waltzing merrily off, her absences - to support her child's additional needs - have been cleared by people who know what they're doing. Luckily teachers don't have to get their absences cleared by parents who think their child should be the centre of everyone's world, not just theirs.
It sounds as though you are fortunate enough not to have to attend appointments beyond doctor/dentist/hair if you truly think this poor woman's a hope in hell of controlling when appointments will me. If they're MDT ones she wouldn't be able to get it budged by a fraction of a second & plenty of clinics run only for a few hours on one day of the week.
You are not wrong to think that adequate teaching should be provided in lesson-time. Demanding extra revision sessions is a bit much though. It is not the teacher's fault that proper cover isn't being provided. Like it wasn't my Physics teacher's fault that my school arranged to have Mr Cadbury's Parrot cover his lessons. My Science grades suffered because I did need the school time to learn what with my home time being quite busy with, er, the home & the running thereof. (Was lovely being told how disappointed the school were I got AA in Science. No, really, telling me I'd let them down by just missing the AA they'd counted on was super.) But that was the school stuffing up. (Something at which they excelled. One of my A-Level History Papers had to be taught to us in our free time because the person meant to be teaching it had slightly less than no clue what she was about & the HoD had to step in to prevent a disaster.)
There are lots of resources out there. Some have been linked to here already, Google will bring you to many MANY more. In Y11 students should (S[E]N aside) have the capacity for independent study & generally not need spoon-feeding, which you give the impression you expect.