I took organic chemistry 1 and 2 over the summer. Each course was about 5 weeks. It wasn't too bad. The lectures were very long though. It was hard to stay focused through all of them. We went usually through at least a chapter per day.
For accelerated courses, I think if you're good at the subject you should be fine. But if it's a subject you know you have trouble with, I wouldn't recommend it because you have to absorb and understand a lot of material in such a short time. It's easy to fall behind if you don't understand something or don't put enough time into it.