These are the exceptions in the grammatical rules around fewer vs. less. Usually we use “fewer” for count nouns (things you can count, e.g., cars, tissues, people) and “less” for mass nouns (things we don’t count, e.g., water, laughter). Time, money, and distance are the exceptions. So, we say “He gave me less than ten minutes to complete the puzzle” even though minutes are countable. Or– “I can’t believe you make less than ten dollars a month selling unicorn popsicles,” even though dollars are definitely countable.