How long do you average per sitting? I try to do 3-4 hours at once, but I can't tell if that's too much or too little. Any input?
I work on it during the day in my free time, and then sit down and do 1-2 hours straight before I go to sleep.
Do whatever you feel comfortable with.
Done 45 mins and are bored? stop and come back to it later, can be a hour, day week, whatever you feel comfortable with. There is no optimal amount, its how you learn and how long you can keep concentrated and retain information being taught to you.
I agree with @benjnev. I think you should just come on whenever suits you and your learning style. Although...
That doesn't sound very good for your health
I personally spend more time on here (discuss.codecademy.com) than on the main site (codecademy.com) because I find that helping other people to learn what I have already learned reinforces my knowledge of the subject. I usually spend 2-3 hours a day on here right now. It used to be about 4-5 hours a day, but I have exams soon so I had to cut down.