I don't understand that.This is what's commonly known as the Rule 0 Fallacy: "it's not broken if you can fix it."
No rule can cover all edge-cases. This is how you get ridiculously complex legalese, because every known hole has to be covered. Which leaves no wiggle room for customisation or flavour changes.
So, its not broken. Croesus wants to not have to track it. He makes a houserule that extends durations for 5 minutes or an encounter.
Frankly, if you've got another encounter within 5 minutes travel time, versimilitude would dictate that it would be the same encounter, because outside of a small set of circumstances, they'll hear that fighting. (I once had a wizard/rogue who researched a wall of silence spell that he could silently cast, to block off noise down a corridor, while he then slaughtered everything in sight.)