You generally should replace them at 80k to 100k, but you can inspect them to get an idea of how f***ed they are and if it’s way past due.
removing the cover and look for the same things as worn or old tires.
Cracking on the side where it turns around pulleys
surface cracks
chipped or missing teeth
threads coming out from the middle
cuts or strips tearing off
press your fingernail into it and it should bounce back and not leave a mark. It’s make of rubber so if it’s not bouncing back it’s rotted.
id you don’t have receipts for the last replacement then plan to do everything including pump tensioner and pulleys (the smooth ones not the cam gears)