Hi fellow pilots
I have a question about it and unscrew the propeller every time I storage my P3A after flying.
How many times can without breaking my propellers in the air, and the bird falls down.
I am be carefull with my bird, so how you can see the need to replace the DJI plastic propellers ...
for example, after 20 flights to use new propellers or after 20 hours?
I have no idea
regards
Rob

I've asked this question in the past and received differing answers.  What seemed to make the most sense was to inspect them for any damage and if you notice when tightening them down, if you have to excessively have to "snug" them down more than usual or more than you have in the past.  Not a real definitive answer but I'm paying attention to the tightness going on and coming off...

I never consider replacing mine unless they have damage.  And if something doesn't seem right with one, they're cheap enough to replace.  

I see no reason to replace them unless a problem is found.  As long as they tighten ok & don't have any chips along the edges or splits in the hub they should be fine.