Hi, I don't have any experience of high sleep needs children (both of mine are low sleep needs, one spectacularly so), but it does sound to me like your LO is starting to need a bit less day sleep. Though if he's catching up from a shorter night the next day / night I probably wouldn't worry too much about it unless his nights are getting super short and he's getting into a pattern of continuous short nights which you can't break.
If it is turning into more than just the occasional earlier wake up, one thing you could try is shifting his nap back a bit by 15 minutes, and keeping his A to bed the same. For example, up until this age I started having to always wake my daughter by 3pm in order to preserve nights, no matter when she fell asleep. Her bedtime was 7.30 at this age, so basically she needed around 4.5 hrs A time in the afternoon. I'm pretty sure that soon after this she started needing an even shorter nap and longer afternoon A time.
Like I say, though, my two are LSN, so you might want to hold off and see what parents of other HSN kids say.
