How long after completing a sale does the buyer have to return or dispute?

[riffmax]

A recent buyer has complained about the item he bought. He has not requested a refund, which he wouldn't be able to get because he told me he made modifications to the item. However, I have a feeling he will try to open a dispute. I can't find information about how long he has to do so before it's too late. I want to hang on to the funds until I'm 100% sure he won't try to pull any tricks.