My 2 month old has started to sleep longer stretches. Not sure if I still need to wake her up every 2-3 hours to feed her or I can let her sleep longer. She is gaining weight appropriately.
You can leave her sleeping at night the same number of weeks. So at 8 weeks they can sleep 8 hs at night (per taking cara babies course). We do that with our 10 week old and make sure she is well fed during the day, which also helps her sleep through the night (per 12 hs by 12 weeks book lol). She is perfectly average gaining weight with this :)