It's very common for LOs to have a mixture of 2 and 1 nap days for a while as they go through the 2-1, so that's absolutely fine if that's the way you think things are going. If you prefer a shorter second nap, then one approach you can take is to set a time for the cn (e.g. asleep by 6.30), and if he takes it at that time you do a slightly later BT, but if he skips it you do an earlier BT. In the meantime you try pushing that first A so his first nap is a bit later, and keep the cn at the same time. Gradually he'll take it less and less often until you're fully on one nap.
Sometimes you find a LO needs a little push to drop the cn too. As you're already on 4.5hrs A in the morning you'll probably find you could skip the cn on occasion and do BT at 21.30 instead and see how that goes. If he can handle 4.5hrs A already he's probably ready for 1 nap now, but it's often easier on the LO to do it gradually with a mixture of 2 and 1 nap days.
The other thing you can try is capping the second nap to 20 minutes but keeping BT the same.
There's a bit more info here
From 2 to 1 nap transition (10-12m and older) and a chat thread here
Anyone want to talk about the 2-1 transition #27
