>distances were always expressed as travel time

I'd like to see more of this kind measurement expression in our modern vernaculars.

For example, an acre could be defined as 43560 sq ft, or 4047 meters, or .405 hectares, but these are arbitrary and don't tell me much. A more useful definition of acre is "the amount of land that a pair of oxen can plow in a day". Then, as a farmer, I don't really care how many square feet or square cubits or square whatever it is. I have a domain-specific (farming) definition that actually communicates something more useful to me than arbitrary distance units.