Well it depends on how often you teach. There is a lot of outside work that is involved with teaching that you aren't necessarily payed for (ex. playlisting, sequencing). So be prepared to spend a lot of time outside of the studio working.
Generally classes are always different because you obviously get a different crowd every time you teach. So being on your toes and being able to read the room is important.
You only spend 2 hours working if you're teaching one class. 30 minutes before class, 1 hour class, and 30 minutes after.