As much as I do wish corruption was more of a thing, I definitely don't think there should be a timer for it. That would suck for people who wanna stay pure because it puts them on a time limit(which kinda just feel bad in most games), and would just lead to a corrupt player just wasting time to cheese the system.
No, if implemented correctly.
Example:
World, on a local scale, slowly become more and more corrupted, everyone trying to do their best to put demonic horse dong six feet under but players character sits on an ass and chew popcorn. As the result when world, on a local scale, become literal hell hole players character, and other, goes like 'faaaaaack, we a loosing up this war...we should abandon our current positions and regroup in the neighbor kingdom/city/etc. for counterattack' -> game over screen with 'I tried so hard and got so far, but in the end it doesnt even matter' leitmotif. Optionally with a 'and than all good united against all bad and won'.
Wanna stay pure -> do something
Wanna become a
bit more demonic -> do something
Do nothing -> gets nothing, no martini no party