I did 9-15 hours a week, plus some volunteering during A levels
I did Psychology (A*), Sociology (A*), Maths (B), Art & Design (B), Critical Thinking (B)
It's pretty easy to work and study provided you're smart about your time, for example, I used to work 5-8 on weekdays and then a few hours at the weekend, so any day I worked in the week I would stay late at college and study until 5, I studied during all my free period rather than spending them in the canteen and I worked out what methods worked for me quickly so I could be efficient. I also got up early every day regardless of whether I 'had' to so I had more hours in my day. I had plenty of time for studying, socialising and hobbies.