When DS dropped to one nap (13 mos), he piddled at the 2h mark for a little bit, but shot up to a 3h nap within 2 weeks of dropping it. Slept 10.5-11h at night, though...
Now, a year later, he does a 2-2h15 nap, same 10.5-11h of bedtime sleep.
Some LOs never hit the 3h mark when they go to one nap, or even 2.5h. If he's fighting bedtime, I'd consider capping the nap (I say that hesistantly for his age...doesn't mean it's not neccessary) or just making sure the wind down is sufficient/long enough.