Hi tulips, welcome to BW.
It's typical for the one nap to shorten with the 2-1 transition. It usually does lengthen, from my personal experience and also from other parents here. Yes, I would work toward at 12 nap by extending 15 min every 3 days or so. We were in this transition for a very long time, in that we were working towards a 1pm nap- a natural consequence as they get older and need more awake time from wake up to nap. Sometimes, we stayed at 12:00 or 12:30, depending on how overtired he was. Throw in teething (canines and molars), and separation anxiety, etc... and it felt like we were always working on some aspect of sleep. I think by 2.5 we were at a 1pm nap, and by 3yo 1:30-2pm naptime.
Around this age, sleep needs start to change... most of the time the overall sleep time shortens. Over time, it can lengthen again, but it depends on the child. What was the average total sleep length before the 2-1 switch for your son? 14hrs?
It looks like he's sleeping 12.5 hrs at night, and 1-1.5 hrs for nap, so 13.5-14 hrs total. This is actually great for this age, unless your son was higher sleep needs. You may find that as he gets older, he will drop his total sleep to about 13 hrs, and once nap is gone, 12-13. You may also find that as you move closer to a noon nap time, his nap extends. And once it does, his night might shorten. If his nap does extend to 2 hrs let's say and ends at 1:30 or 2, you can adjust BT accordingly... closer to 7:30.
