Start right away! My LO really took to EASY right from day 1. I'm almost sure that because of EASY, we never had long awake periods at night: he was used to his daytime routine, and our nighttime feeds were different, and he went right back to sleep. When he got to be 3 months old we really started having regular naps at regular times, but before that it was all about keeping him on a regular routine, regardless of the time. It helps SO much, and helps mom feel like there's SOME order to her life!