Wake a newborn at night?

My baby is now 4 weeks old. She is really fussy in the evenings but when I get her down to sleep she will stay asleep! I've never let her go over 4 hours (until now, she slept 4 1/2 and went 5 hr between nursing) I will usually end up waking her to eat but then she isn't hungry/falls asleep when I nurse her then she will wake up on her own 2 hrs later to nurse. I was reading that once your baby is 4 weeks old you can let them sleep and wake themselves to eat. Should I wake her at so many hours between nursing at night or let her sleep and wake herself to eat?