Hi JulieNG
I have a 4 mo too and she's on a 6/6 schedule, but on a 4 hr EASY - I'd like to know the answer to this too as I'm not a morning person!
If your lo is 4 mo, he'll def. want the last catnap because he won't have had as much sleep during the day. When they're on a 3.5 hr EASY, I'm pretty sure there is no catnap, just 3 1.5-2 hr naps during the day. (That's what I did while I was on 3.5). In any case, would love to know the answer to changing a schedule - hope you don't mind if I tagged along on this. :-)