I think with BW, there's a lot of flexibility in that your days aren't so much a timed schedule, but a routine that's normally done in similarly timed chunks. That said, if some times he sleeps for 2h15 minutes one day, or 1h50 minutes the next; as long as he's happy, thriving, doing well, I think you're responding well to his needs!
My son is now 5.5 mo, and one of his naps tends to be longer than the other (pm nap). All babies are different, and they don't necessarily fit in the "mold."
It sounds like he's sleeping well at night, so I think if you feel like he's a happy little boy, then you're good to go!
If you'd feel better with posting your routine, we can see if anything is going on.
HTH! Let's see what some other moms have to say, too