hi, I have a 3 wo one too
for us it's around 1 hr from the moment she calls for me until I put her back to sleep [which takes 15~20 minutes, then she naps 45min~1,5hrs or even longer if on the go, but I try to wake her so that she doesn't really miss feeding time too much, she's breastfed].
If I try to put her down sooner than after 1 hr, she'll just take longer to fall asleep.
BUT all babies are different so you really have to watch for the tiredness signs. It might even be that your Lo can only handle feeding and nappy change. You might want to try putting him down sooner, before he yawns and see if it helps him nap longer.
Anyway, it's a struggle at this age
some of our naps are great but most of the evenings are terrible [she gets overstimulated by her daddy and big sister
] so if you're having a bit of a hard time, don't worry, it gets better