UV light is damaging to all plastics.
I'd say DJI would use UV stabilisers in their plastics (body shell and props etc).
This prolongs the life of plastics in the sun, but it will eventually get to them and make them become brittle.
The strongest UV light is through the summer and part shoulder months, most of the remaining year (perhaps 7 or 8 months ?) the UV light rating is usually in the low to moderate range.
But (well formulated) plastic degrades over such a long time, considering flight times and relatively short exposure to harsher sunlight.
I'd say on an average flight out, it'd be on the ground ready to fly or after landing, or in the air flying for maybe up to an hour to an hour and a half.
Topping that off, I'd say I fly mostly early to mid morning, or after mid afternoon through to dusk, when UV light is even lower.
I have never changed my props on the M1P as a precautionary measure, only upgrades, like changing from 8330 stock props to 8331 Platinum props, and then again more recently to MAS props.
That alone means I have changed mine 3 times in 4 years.
I just check mine (often not EVERY flight) for chips and cracks, obviously if I ever fly into light foliage or clip some long grass, of of course have any sort of minor crash, I'd be checking them even closer, and considering changing them depending on the situation and incident type / severity.
There's two phrases that come to mind...
But they contradict each other.
"If it ain't broke, don't fix it"
"When in doubt, change em out"
It's up to the pilot I assume
You're so right there, and funny how if any doubt exists, pilots sometimes just don't want to waste props, a mere approx $20 for 2 pairs of OEM props, just to be sure.
Why my original 8330 props are still in my bag, even though I know that will NEVER fit them again due to the benefits of the 8331 and MAS props.