I think that, even on 3 hour EASY, your baby will sleep for longer stretches at night. Tracy's book suggests you transition to 4 hour EASY at 4 months. Her third book has a good plan for making the change (I'm trying it right now). In it, you spend about two weeks gradually moving your baby from a 3 to 4 hour routine. If you have the book, it's on page 230. If you don't, there's a post somewhere around here that has a link you can print the page from.