He's really young to be consistently on one nap so be on the lookout for OT.
One one nap, the nap usually needs to be at least two hours, often more - to keep to a 11.5-12hr day.
When my daughter was first on one nap we did 2 x 4.5hr A times, otherwise she quickly got OT. So we would do
7am awake,
11.30am nap 2.5-3hrs
2pm awake
6-7pm (depending on nap) asleep for the night.