Each lo is different so it's hard to tell if your lo is ready. However, most babies at 4 months are ready to transition to a 4h EASY. For us, staying too long on a 3.5h easy caused some night wakings (lo had been sttn already). I also noticed that my lo was no longer interested in feedings that much. That was probably my biggest sign.
Unfortunately, the best way to see is to try it out. I would recommend adding 5/10 minutes to the first A time for 3 days. After that I would do the same to the second A time and so on. There are some threads on this but I don't know how to link them. Maybe someone can explain or post them. My rule was always if my naps start being 30 minutes she was not ready.
hth
