Hi C-Line... well, I see your dilemma even though many would envy what you have. Technically your son is getting 11 hours of solid sleep which is fantastic. (I think 11 1/2 is ideal according to different things I've read but that's just a guideline) First of all, I think it's great that he can amuse himself in the morn and that you don't go running in....this will certainly help things.
I think you just need a little tweaking to shift his sleep phase...maybe if he went to sleep at 7 he'd sleep until 6 but then again.....however, I know you've said you've tried this but I'm wondering if you've shifted his naps/meals/activities too when you've done this or just the actual bedtime.
Looking at your schedule a few things stand out which you've actually noted. First of all his first nap is way too early. I know, it's hard to keep him up until 9 am when he's waking so early. If you do this in increments though it should work (it did for me anyway) Maybe if you put off his 7:30 nap by 10 or 15 minutes each day, it would help. If you could eventually keep him until 9, then he would wake later which would result in a later second nap. Could you find some sort of low key activity to do to distract him? A later 2nd nap would result in the elimination of the third nap and should hold him until bedtime. You just have to be careful not to do this too drastically or he could get overtired (as you've mentioned) and start having too short naps. Ideally, if you could get that 2nd nap to start around 1 or 1:30, he'd be up by 3 and should be okay until bed at 7. Does that make sense?? I think I tend to ramble and repeat myself.
Or I suppose if you do want to keep the third nap and not change the other ones then definitely don't let him sleep the full hour. Right now he's getting 5 hours of day sleep which I think maybe a bit much (but that's just me....you may want to check with one of the sleep moderators) As for this week, you may be right, maybe he is telling you it's time to cut the cat nap (I think 8 months is a good/usual time)
As for wts, I've never done it but I've heard a lot of good things about it. If you are hesitating to mess with his naps then maybe this is the route for you to take. Afterall, you need to be comfortable with the strategy. Do you have Tracy's newest book (big and hardcover). It has a section on WTS under habitual waking (one of the 6 reasons for disturbed sleep) I'd give you the page number but I lent out my book. I'm not sure if her first book (softcover) addresses it. Maybe if you start another thread asking for help on how to do WTS you'd get some insight. Anyhow, I hope this helps. Let us know what you decide and how it works out!
Zelka