How long do you let your baby sleep at night?

No joke my son fell asleep after I fed him at 9 last night and i had to wake him up at 7 this morning to eat. I mean so many people say to let them eat on command but I’m worried that sometimes he just doesn’t wake up if he’s hungry. His “normal” night is eating every 2-3 hrs until midnight and then he sleeps until 6 and from there eating every 2-3 hrs again. We haven’t been to the drs since the first week after he was born and we’re scheduled to go this Friday when he’s a month old so I’m not sure whether or hot he’s gaining weight. We’re breastfeeding and supplementing with formula. And he’ll go for 20 minutes on each breast. He would eat longer but the pediatrician told me to stop him after 20. This is only the 2nd time he’s slept that long and I know some people say to just let them sleep at night but 9-10 hours straight is quite a lot!