My LO was born at 34weeks. She is 7 weeks tomorrow. At 6wks dr said we could stop waking her to eat (we were having to every 3hrs since she was a preemie). She now goes between 4-5hrs most of the time. She used to feed for 25-35minutes. Since switching to on demand, she will only eat for 10-20. I feel this is odd since she is going longer between feedings? Is she just becoming more efficient the older she gets? I'm not concerned about her not getting enough, she has almost gained 2lbs since birth. Just curious if this is normal.