I know from bitter, painful experience that you shouldn't pump longer than 20-30 minutes at a time, maximum. I spent months with raw, bleeding, painful nipples from doing 2x 1 hour blocks of pumping per day. Now I do 3 or 4 30-minute pumps and my boobs are thanking me for it!
Are you massaging and doing compressions to help empty your breasts? You will get more out in less time dong this.
Do you have any sore or hard bits on the leaky side? I ask because these days I only ever leak when I've got a blocked duct, and it gets all hard and sore and the milk tastes salty. Heat, lots of massage, and pumping little and often is the best answer to that, I find.