Are you meant to be working towards 4 hrs AT 4 months or start transitioning when they turn 4 months?
I've had this question myself in the past because it is the 4/4 4hr EASY at 4 months but in one of the BW books Tracy wrote that LOs were ready to move to the 4hr E during their third month which to me means during the time from 3-4 months but mostly here on the forums we say it is at 4 months and during the month from when LO turns 4 months.
Unfortunately as Tracy is no longer with us we are unable to ask for clarification BUT as with all things BW Tracy taught us to listen to our babies so really it matters very little if baby is exactly 4 months or a bit over or under, so we can manage without exact rules as we follow what our individual baby needs.
Tracy also said some babies are not ready for the 4 hr E until closer to 6 months (or at 6 months), she mentioned prem and low birth rate, and BF babies may not be ready to move to 4hrs. My own DS, not prem, not low birth weight and not BF could not go longer than 3hrs between E until he was 6 months old. He just couldn't. Once he had solids between his milk feeds he was able to extend the time between milk feeds up to the 4hrs.
On the flip side I've seen on threads LOs who have had a stay in hospital at birth and been put on a 4hr E routine from the get-go as that is what the hospital has done.
If he can go longer than 3hrs then his nap time won't bother him. He will not wake hungry just because you expect him to eat at 3hrs, if he is asleep he is more likely to go over 3hrs for E and be hungry after he's finished sleeping. This may mean one or more feeds goes longer than 3hrs whilst the others stay at 3hrs for instance. It's fine. You don't have to wake him at the 3hr mark to feed him, just wait until he wakes. And if you continue with the sleep training he is likely to get a longer nap and one that is not broken or disturbed.
if he goes over the 3hr mark and is sleeping then you feed when he wakes, you can count the next E from that time, so see the E time and add 3hrs this is roughly when he will need to eat again unless he is asleep. if you end up in a position where E comes just before a nap try to give the feed a touch earlier so you avoid a feed to sleep habit.
Does this help?
The BW routines are not hard and fast, they are very adaptable for the individual needs of the baby.