Hi! I just want to jump in so I can follow along as we are in the midst of the 2-1 as well! H is 14 months, we've been doing the 20 min nap for about a month now. We get a 1.5-2 hr pm nap but we still get 10.5/11 hrs at most at night. Comes with the territory I guess!
Kara, sounds like we're in the same position as you! Unfortunately we get a 6am wake up 
But we make H stay in bed until 7 and he usually does well only crying out on occasion.
What is the next step after the 20 min nap? H does between 3/3.25 hrs after his 20 min nap and then 4 hr to bedtime. He goes to bed really easily so I can't imagine he needs more A time before bed. I don't know if bedtime gets pushed back or am nap gets cut. Seems like we run out of hours in the day!
After the 20 minute nap, the next step is usually to drop that and go to one nap! I kept with the 20 minute nap until the day when DS just refused it, and put him down later on for one nap, albeit a bit early in the day.
So if he is doing -
First A 3 - 3h30m
nap 20 min
Second A 3+h
nap 1h30m - 2h
Last A 4h
Bed
Then what will likely happen is that one day he just won't go down for that first nap, and then you abandon at a certain point in time because it starts to get too late for that little catnap, so just don't bother with it! He will then likely be ready for sleep sometime around 4 - 4.5h A time and will hopefully sleep a minimum of 1.5h, but really what you need to make it through the day is 2h....but that can take a bit of time for him to lengthen that out. And, then bedtime might have to be earlier, 4h after he wakes from that nap, even if that is early in the day. Hopefully he will make up the missed day sleep by tacking it on to his night.
We were fine on that for a few days and then DS was shattered in the morning at his old catnap time (930-1000) so I would let him have it. And then a later 1.5 hour afternoon nap. For the first two weeks or so I watched him carefully to see if he was tired for the catnap or not, and if so, then I put him down, if not I held off for nap until 1100/1130 and do an early bedtime (530/600) if he didn't take a 2 - 2.5 hour afternoon sleep. I think there were more days WITH the catnap than without. So he would sort of do a one nap day every 5 days, then after a while it became every 4 days, every 3 days, every second day and so on. Now he is onto one nap, with a two nap day happening once every 6 or 7 days.
Hope that is helpful!
