Power pumping question


I’ve got twin preemies who are still learning to latch. We are working with a lactation consultant but the babies are going to need some time and in the meantime I’m pumping like crazy trying to get my supply up. I’m pumping 8+ times a day and one of those is a power pump. My supply is on the low side - I get maybe an ounce per pump. My lactation consultant suggested 10-15-10-15-10 for a power pump but I’m usually still getting milk out at 10 minutes so I don’t want to stop pumping. Should I stop at 10 minutes or should I go past when I stop expressing milk? When I do a regular 20 minute session I usually have a second let down around 12 minutes. Thanks!