I always pumped 5 minutes after my min stopped, that should be plenty to help keep signaling your body for more milk

I’ve pumped for my daughter for 12 months and I’m currently exclusively pumping for my 8 week old and I’ve never pumped longer than 20 minute sessions.

Do you also BF? I've heard pumping for a bit after helps increase supply. I exclusively pump and go for 25 minutes. Sometimes I'll get a second let down which is why I pump so long. On average I'm pumping 4-6 oz on each side.

You could try pumping for 20 mins or 25 for a week and see how it affects your supply. If it isn't helping, you can go back to pumping longer and it should go back up. I can't tell you either way what would happen. But try it and record how much you're getting and then compare it to what you were getting before.