Hi Sarah, sorry for the late reply too
He's over 11mo now isn't he hun? 3.5hrs is on the lower end of the average A times but not heard of. How do you feel he is during the day? Do you feel he's OT, or is he generally happy?
Some OT will happen during the transition to one nap. It is to be expected, but as you said he doesn't handle it too well, we can take the softly, softly approach. No worries at all.
Ok, so if we work that a 6.30am wu is the ideal, we take it from there. If he's waking happy and playing around in there, I would just leave him as long as possible or close to the ideal wu. If he's waking upset, do what you usually do to soothe a NW and treat every wu as a NW if it's before 6.30am. Then we set the nap at 3.5hrs A after 6.30 irrelevant of what time he woke. The down time in bed won't really count as A at this age as it's not too stimulating. So first nap at 10am. I really think pushing this one out will help with the 5am wu. It did with us. For the nap, I would do w2s at around 25mins, so go in and gently stroke his cheek or hold his shoulder until you hear a little sigh or breathing change, then slowly back out of the room to see if he transitions to the next sleep cycle. This may take time to get right. Also it might not work if the A time is too short, but this will help us understand more yk? I think we have a better chance of making this nap a long one than the afternoon one.
If the nap is short, I would try the above again at 3.5hrs A. Again, just to see. Otherwise of the nap is long, I would still do 3.5hrs and expect a shorter nap as that's ok with the length of day you want.
More tweaking will be needed hun, but I think this is a good starting point. We'll know more once you try this for a day or two. Log everything including any NW's for me ok? Really gives us a full picture.
My DD wouldn't sleep in the buggy either, or be apop'd if she wasn't tired enough, so don't worry. We can make a plan for that. Xx