Aishi, if you think he needs a longer day, then I would try for bt at 6:30 to start with on a nnd. It is going to be difficult to get a real routine going if some days he naps for 1hr20 or longer then some days he doesnt. You did say he gets quiet time on nnds tho right? I think that would be key to keeping him on the best schedule possible. Put him down the same time every day and then adjust bt to whether or not he slept. I agree some of the nw's could be habit now, so in that case unless he cries for you, I would leave him to ss and hope he gets over it and starts sttn again.
gwcarnes, If you want an earlier BT the other option is to cap the nap. Have you tried that? I try to look at things with M as if it were me, if I had a 2hour nap during the day then I know I would be up later at night, but with only a short 30-45 min nap I wouldnt be as rested and I would probably go to bed around the same time, maybe a little later than if I didnt have a nap at all.