I personally wouldn't start capping the first nap until you've dropped the third, which usually happens once the A time gets to around 3h. So you may be close. Don't be afraid of slightly shorter nights during this transition, you may just find you have a little more flexibility if you're not tied to strict 7pm BT. Then of course you may need EBT for a little while once you're down to two naps. Also I think if you're a bit more flexible then you may find he can do an earlier, longer nap later on in the day after a short first nap, if you need to. Sorry I don't know if that makes sense, I mean you might be able to compensate for the short first nap by reducing the following A time a bit in the hope of a longer 2nd nap, even if that fails, you still have time for a third, which could even end up being the longest nap if it's early enough and he needs it. But I really would continue to work on pushing out that first nap, in the long run that should help to sort out the rest of the day...