Have you noticed a difference between how quickly he falls asleep on long nap days as opposed to short nap days?
My guess is he's still adjusting to 1 nap. Some days he's just tired enough at noon, and so has a nice long nap. Some days he's slightly overtired by that time, so short naps. That's natural and normal -- he's still stretching into a 5 hour A time, and so depending on how his night sleep was, whether he's teething, has a growth spurt, or who knows what secret toddler thing is going on he makes it on some days and doesn't on others.
I think I'd keep some notes for a few days, and see if there's any difference between the bedtime behavior on short nap and long nap days. I suspect he's OT at bedtime -- perhaps on both days! Putting to bed at 6:45 probably didn't make a difference as he needs more like 30-45 minutes earlier to probably kill the OT probablem. If he wakes at 1 pm (a 1 hour nap), then you want him ASLEEP no later than 6 pm! If he wakes at 2/2:30 (2-2.5 hour nap), then a 7 pm bedtime should be sufficient. If it's not, you can try 6:30 and see if it works better for him.
One thing that I finally figured out with my son is that he needs *less* A time in the afternoon as opposed to the morning. So, even now at 2.5 y.o., he only has 4.5 hours of A time after his nap before bedtime. More than that, and we get EWs. You may want to go with a SUPER early bedtime for awhile and see if that helps the falling asleep thing.
Of course, if it's not broke don't fix it! In other words, sounds like you're getting 11 hours of sleep at night which is great! No NWs/EWs, and I'm not sure I'd worry too much. I think I might play with that nap a little bit -- maybe watch really closely and see if you see any sleepy signs on short-nap days to show that he's OT by noon -- just to lengthen it, but other than that you mgiht just want to hang out and wait for him to grow into the A time a bit better. My guess another month or two and you'll get consistent long naps and a more easy bedtime! (Long post just to say might as well keep it all the same!
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