Nighttime sleep...

My 4 week old often sleeps 5 hours at night, then wakes to eat and then sleeps another 5 hours. Last night she ate at 10:30pm then I put her to bed and she didn’t wake up until I woke her up at 6:45am to eat and then she slept until 11:15am again after that. Obviously the sleep was wonderful for me, but I know she’s still very little to be sleeping that long. She is growing fine, has plenty of wet/dirty diapers and is gaining weight. Last night may have just been a fluke, but is it ok to let her sleep for long stretches at night as long as she is healthy and growing fine? She eats about every 3 hours during the day and usually at 8pm and 10pm before bed. She is exclusively breast fed if that matters.