FWIW my DD takes a long time to settle at BT. I used to worry and stress about it and try changing nap length and BT and our wind down, etc, etc. It wasn't until she had a few days where she went to bed an hour or so later because we were out and she still took ages to settle that I realized it's just the way she is. It does not matter when BT is, it takes her 30-60 min to settle to sleep. Last night BT was 1 1/2 hours late and she still took an hour to settle down! Could your LO be the same?
DDs nights also shortened at that age. For her, part of it was teething causing the EW. A developmental leap could also be part of it. Like Lindsay said, 12 hours sleep is pretty good so I wouldn't worry too much especially if he's generally happy when awake. Honestly, now that I have a second and I don't have time to worry about DDs sleep I can see that her sleep was almost always ok and I was anxious over nothing. All you can do is offer opportunities to sleep - it's up to him what he does with it.