how long do you pump for?

How long do you pump for? I have not been pumping regularly yet, but I do ebf. I maybe pump 3-5 times per week, sometimes after feedings and sometimes in between feedings. In less than 5 minutes I get one ounce from each side, but that is it. After that it is dry, even if I pump for 10-15 minutes more. I would like to build a freezer stash, but since I am only finding a few times a week to pump, it is going very slow.