early on yep the rule applies-for sure until your milk is in. my little guy didn't sleep for more than three hours at a stretch at night until week 6! but they know what they need when they need it!
My pedi said not to wake him during the night. She said to only apply the 4 hours rule during the day. If he sleeps @ nite, let him sleep. If your BFing i would pump @ least once during the nite to keep your supply up.
On the advice of a nurse at the hospital, I feed every 2 to 2.5 hours during the day and wake him if necessary. This gets me about 4 hours of straight sleep at night.
Re: the 4 hour sleeping rule?
Just be aware that if you are BFing your supply could suffer if you don't at least pump during the night.
I second this. We are lucky to get a two hour stretch of sleeping at night.