Hi, Ive been pumping for two years now and Ive tried a bunch of times.
For me three times a day about 4 hours apart for 20 to 30 minutes a session.
Sometimes I go crazy and pump for much longer but the last time I did this...yesterday...I ended up with water blisters.
Somewhere on this site DiDi posted a great summary which I reccommend. She has had great success.
I wish you happy pumping and growing!
Owlie