Letting baby sleep

How long do you/would you let your 1 1/2 month old sleep at night until they eat again....till they wake up on their own or after a certain time? A few weeks ago when our LO wasn’t gaining weight fast enough her doctor told us to wake her up after 6 hours if she doesn’t wake up on her own. Well now she’s catching up weight wise so that isn’t much of a concern now. So idk if I should still be waking her after 6 or let her go till she wakes up. My husband thinks we should just let her go but I’m on the fence....guess if she was that hungry she would be waking up 🤷‍♀️ We have been blessed in the fact that she sleeps 6-8 hours at night.