Is it because of the "than"? Do we just not like saying "fewer than"? Because it wouldn't offend my ear to hear "we need less than 5 chairs", but "we need less chairs" is outrageous to me, (for less than however many chairs it takes for them to become dequantized) [I did it again there, did you notice?]
Or maybe it's to do with the minutes being a quantization of something continuous, whereas usually we deal with the transition the other way.
"couches vs. furniture" couches are discrete, furniture is discrete things as a collective.
"time vs minutes" time is continuous, minutes are a quantization of it. That is a difference compared to couches/ furniture. How do we talk about other quantizations of continuous?
Distance: how far is it? Less than 5 miles. Maybe it's an acknowledgement of the fact that we talk about miles but inherently understand that distance isn't countable.
Oops that used "than" again. Uhhh... "the battery in my electric car is degraded so I get 10 less miles per charge". Hmm I'm not sure if that sounds right....