Dana, unless he was a low birth weight baby, he should be able to go 2.5-3 hrs between feedings. And, yes, as time goes by, he'll be staying awake longer, and you'll be able to notice his transition. He won't want to go to sleep at his previous nap times, he'll be less hungry at 3 hrs and ready to last a little longer. But it doesn't always happen at 4 months; sometimes babies don't go 4 hrs until 5-6 months. Any change in his routine though should be gradual. Try spacing out his feedings in 15 min increments every day or so. If you need to, give him a pacifier to hold him off, but don't hold him off to the point of sheer hunger. Just take it slowly, day by day. As for the routine becoming more set, I found that it changed very often until about 8 months, then the changes were less drastic. But change can be expected for a long, long time.