With a 4.30am start no he won't make it on one nap, but allowing him two naps to catch up is probably fuelling the early starts. Some LOs do keep 2 naps until 18 months but they are generally very high sleep needs and/or having short nights. 12 months I would say is fairly common, I read somewhere 15 months was average.
My suggestion would be to push out and cap the morning nap shorter - so 9.40/45-10 - for a few days and then if you get a better WU one day (post 6am say) then push him through to one nap at 11.30am or as close as you can get to it and allow to sleep up to 3h, bedtime as early as necessary. If it's a total mess of a nap then try to get a late afternoon catnap, failing that super early BT. What do you think?
It doesn't have to be one nap every day, but some one nap days may make him tired enough to sleep in
