I have a game designer or programmer way of looking at it, which I want to call out because it means I am thinking about it in a specific way that many players will not. Also, I am not saying the way that I am thinking about it defines the right way to have fun. With that aside -
Concerning a prototyped mechanic, one cannot just conveniently ignore valid cases that one dislikes. That isn't good, intentional design. We have discussed 600 rounds for the sake of emphasis, but as you say even 100 rounds would be extraordinary. That means there are a lot of cases in the volume of state-space that the prototyped mechanic defines, that are extraordinary.
So while it is true (for the sake of argument) that 59 minutes of walking and 1 minute of combat will break a rest, while 59 minutes and 30 seconds will not, nor 58 minutes of walking and 1 minute of combat; it is also on the table that 599 rounds of combat will not break a rest. That's one of the cases entailed by the mechanic (as you read it). And 299 rounds of combat also won't break the rest, even though that is very far within the envelope!
Given that game rules are interpreted we can always consider our options for interpretation: the RAI. If a valid interpretation (such as one cleaving to the literal meaning, but grasping the other horn of an ambiguity) exists, that does not contain such undesirable cases, then we can prefer it. It serves as a razor - alongside Occam's Razor and others (which JC's ruling eschews of course!)