Maggie---The deep sleep usually happens for the first 2 to 3 hours after that they cycle out to a lighter sleep. When my dd transitioned to one nap she would, like clock work, cry out when she cycled out of deep sleep into a lighter sleep after 3 hours but if I went quickly in before she was fully awake and put a hand on her then she wouldn't fully waken and settled back in. The wakings later in the night were harder to deal with, unfortunately.
Given your lo's schedule, the early wakings and the fact that he's transitioned to one nap a few months ago makes me think that the problem is that you actually need to push the nap later. He has only 4.5 to 5 hours before wakeup and nap and most lo's around your ds's age need about 5.5 to 6. the fact that he only sleeps one hour occasionally also makes me think he needs a later nap. I read in one of the sleep books that the ideal nap time is the halfway mark of night sleep moved forward 12 hours ie. if he sleeps 11 hours from 7:30 to 6:30 the ideal nap time is 1 o'clock (5.5 hours) so you may want to try to move the nap slowly closer to that mark.
I know it's hard when they're tired and it seems counterintuitive but it's like that post on the general sleep board about how Tracy solved 45 minute naps--you actually have to push naps back so they are tired enough that they will take a long restorative nap.
Even if he gets a 2 hour nap it may still be too early because he is then not sleeping again in the evening until 6.5 hours after nap wakeup, if not more. That is probably too long an afternoon A time and he is overtired at bed. With my dd if she was overtired at bedtime regardless of the length of her nap that day we would get night wakings. Most lo's do better with a slightly shorter afternoon A time than morning ie. 5 to 5.5 hours.
What I would suggest is to move bedtime at least 30 minutes earlier to see if that helps with the night wakings and early wakeups. The increased (and better) sleep at night should help your son be able to move his nap back. I would try it in 15 minute increments every week to see how he tolerates it.
Frances--Actually night terrors, conversely, only happen within the first couple hours after falling asleep since they are when your lo transitions between sleep cycles when she is in a deep sleep. But you are right, there is a lot of research showing that night terrors improve substantially when bedtimes are moved earlier. (see Dr. Greene's website, for example)
I recently bought a really good book call "Better Sleep for your Baby and Child" by the neurologist who heads up the Sleep Disorder clinic here at the world renowned Hospital for Sick Children in Toronto. Not a sleep training manual but some excellent, reader friendly information about children's sleep, if you were interested in reading more about the physiology of sleep.
HTH
