My first was an incredible sleeper from the beginning. She would have slept 4-6 hours immediately I’m sure. The doctor advised us to wake her to feed until she reached her birthweight again though (maybe because she went from about 8 lbs to 7 lbs after a couple of days). But once she regained to her birthweight after about 10 days, the doctor said let her sleep. She immediately started sleeping 6 hours a night. It was alarming to me but she gained well and did great. She is now almost 6.