Wow, he still takes two naps at 20 months?!? Lucky! My daughter was down to one nap by 9 months. And dropped that at 18 months. Now she's 2.5 and has actually slept all night a couple of times.
And I totally feel your pain, because my daughter always went to sleep at 11 until she dropped all her naps. Didn't matter what I did or when we started bedtime, she couldn't sleep before 11.
Anyway! Enough about my kid, lol! Here are my thoughts for you. It sounds like he really doesn't need that second nap but it'll be a little while before he's quite able to make it through the evening comfortably without it. So the first thing to do is to move his bedtime earlier--maybe 7 or so. At first he'll probably do the power nap thing and wake up after an hour, because he's used to waking up after an hour, but you'll just have to stick it out a few nights--and experiment with the time--until you figure out what time he can go down and still sleep through. And you might need to keep him up after he's tired at first. At least that's what I had to do with my DD. I finally figured out that if she went down before 6:30, she was going to wake up again and be up all night, so I just had to keep her up till then. There were nights she was falling asleep at 5 and I would put on a movie to keep her awake (yes, movies keep my kid awake
), but after her body adjusted I stopped needing to do that anymore. Now she usually goes to bed around 7:30 or 8 and sleeps (with a few wakeups) for close to 12 hours. (And yes, that's my idea of GOOD sleep for her, and yes, I know that's kinda sad.
The other thing I would do if I were you is try to move his first nap later. It sounds like you kinda need him to nap that early for your family schedule, but 11:30 is pretty early for a single nap IMO. Most of DD's friends (who still nap) go down more like 1 to 3 and then bed at 9. Maybe even something like 12 to 1:30 would work better? Does your DH have to walk out the door at 1:30, or could he possibly let DS sleep a little longer? My DD likes to sleep late in the mornings, so if we have to be somewhere I will frequently take her straight from bed to the car and put her in the carseat still half asleep. I'll have a snack with me for her to eat once she's awake enough. She wakes up when I put her in the car, but that way she gets to sleep right up to the minute when we leave, and she kinda relaxes in the car. She goes to school 2 days a week, and frequently I take her in her pjs and then change her in the car once we get there!
Maybe your DH could gradually move naptime to 12:30 and then let DS sleep until 2 and then take him straight to the car and have a snack for him to eat in the car? That extra half hour later might make it easier for him to last a little longer in the evenings, and then he might even go to bed for the night around 6:30, once he adjusts to losing that evening power nap.
You could also try encouraging your DH to actually get him out of bed at 7. Sounds counterintuitive, I know, but waking up in the morning--and getting up and outside, preferably--sets your body clock for the day. Cut out any tv if he's watching any, especially in the morning.
Good luck! And seriously, he's not a bad sleeper at all, mama! Sounds like he's getting LOTS of sleep, even though it's not quite at the best time for it, but stilll, enough sleep is a really nice thing--believe me!