M.H.
First you baby can go as long as he can go without nursing. At 3 mos its on demand. Thank Goodness for a sleeper, don't EVER wake a sleeping baby to eat unless he's under weight/nourished. All human milk is different and has different density based on your particular child's need. My kids never took more than 3-4 oz at a time (expressed, when I was at work) and they have always been in 95th percentile or higher for height and weight. With my oldest he ate 1 side for 10 min at nearly every feed, while my baby was more of a lingerer and liked to do both sides for 10-15 min each at every feed. it all depends on suction, flow etc and that is different for each child.
Second use this time to store a little extra milk by getting up to pump at night, when he's sleeping. You never know when your supply may start to dwindle while you are working, so a this stage you can never store too much.
Trust the process, this nature at work. You're doing a great job and as long as he is satisfied and gaining weight, follow his lead!!