I cancelled a dispute when it sounded like a seller was responsive, and would actually ship my item.

Unfortunately at that time, E-Bay didn't have a method to postpone a dispute. I don't know if that has changed.

Anyway, I was lucky, about 3 months later, my item did finally arrive (after I had given up and bought a second one).

So... as others have said, cancel the dispute once you have the item in hand. I think you can leave the dispute open without progress or actions for some time.

Perhaps you could reset the 30 day count by cancelling the auction, and having the seller re-up the auction as a "buy-it-now".