Until DS started school last year I had had nothing to do with education since I left school in the mid 80s. I became a parent governor last year and it has been a real eye-opener.
During their summer holidays the teachers, among other tasks, cleared their classrooms, made and set up new displays, lesson planned for the new curriculum and redecorated the library and main corridor.
I saw the training schedule for the last INSET day. It is far from a waste of time. It's an early start with four or five subjects covered, not finishing until well into the evening.
Teachers also attend courses and other meetings off site at the end of the school day. That might be where your child's teacher is going when you see them 'buggering off at 3.30'.
Every meeting I have been to with teachers present has been before or after the school day. I get there for an 8am meeting and they've been there since 7am. They often have to stay for meetings that start at 7.30pm to fit in with the commitments of other members of the governing body.
Then there are the additional day to day and week to week responsibilities they take on, such as lunchtime and after school clubs, sports teams' fixtures, staff meetings, frontier trips...
I don't know any teachers who take 190 days of their annual leave.