The rollers should be checked at every belt change---not replaced unless bad.
Spin the rollers and feel for grit, wobble, pull and tug.
The Porsche Dealer suggests every 60,000 miles to change all rollers.
Porsche also has a TSB-technical service bulletin on the cam belt tension roller:
The cam belt tension roller is OK if it feels loose or "noisy"---But monitor closely.
Clarks suggests every 90,000 miles----(every other belt change 45K + 45K =90K miles)
I change the belts more often and sugest you use the 60,000 mileage as a guide.
Per Clarks:
If you do not have service records, change the rollers.
Get the full belt and roller Contitech kit===Pelican Parts.
The updated WaterPumps need the 46mm cam tension roller kit.
GL
John