When is the correct time to replace my bio-max media rings to my fluval 405 aquarium filter?

There is no "correct time". I would suspect that their lifetime would be many years. The media rings should only be replaced if they are decomposing or are totally blocked and have lost all their ability to house the bacteria that forms as and where they are supposed to. The normal thing to do is to wash about 3/4ths of them well and then only rinse the other 1/4 before putting them back to work in the filter thereby keeping the cycled bacteria alive and working.