My #1 bass (2023 Fender Player Jazz) has a pao ferro fretboard. I like it quite a bit, but I’ve never before had a bass with a pao ferro fretboard.
So… how often should I be conditioning the fretboard? Should I be doing it regularly? How do I tell when it’s time to condition it?
Usually twice a day, 
If it’s indoor maybe once a year.
My two Mayones have Pau Ferro fretboards, and the basses never leave my music room. They each get plenty of play.
I put a drop or two of F-One on them when I change their strings, which is not very often — at least six months or more between changes of TI Jazz Rounds. Their fretboards are in fantastic shape.
Just spitballing but some of that is going to depend on the climate where you’re at. For instance, here in Colorado it tends to be pretty dry (10 - 15% humidity) a lot of the year. I’ve been trying to make sure I hit my fretboards up to oil them every 3 months or so.
Yep, humidity mileage can vary. But so does the age of the fretboard material, i.e., aged wood will not react as much or as often to humidity changes relative to less aged wood that is not as dried out.
That said, of the dozens of guitars and basses I’ve owned over the decades, there’s not been one that experienced any cracks or adverse effects from lack of conditioning. It’s pretty far down the maintenance totem pole compared to other considerations.