I think ideally, you should be AIMING towards 1 hour 15 minutes. If you allow yourself 3 hours, you will take 3 hours, push yourself and you'll be surprised how quick you get them done.
I can do sets (with tips) in 50 minutes if I really really push myself but my general pace is 1 hour 10 mins so I book out 1 hour 15 just to meet & greet/ toilet break etc.
If you're really struggling, write down how long each step is taking you and try cut it down from there, 3 hours is pretty long, even for a beginner - our lessons at college were only 3 hours and the majority of us managed to get a set done in that time - we 'failed' if we took longer than 2.