How long do/did you breastfeed your 2months old?

I’m aware every baby is different but I just wanted to have an idea of an average duration. I had been pumping most of the time in a day and latching on my breast once or twice a day but now I’m planning to exclusively latch and see how he does. He takes in about 4-5 ounces every 3-4 hours. I’m not at all sure how to count breastfeeding time. He latches well but keeps falling asleep within 5mins of starting so I need an estimate to keep him on it until I know he is full. I’ve tried keeping him cooler to make him stay awake but he still dozes off.