It took me less than 2 seconds to spot this error on Yahoo! Style:
Lots of people know that when you’re talking about countable things, you use fewer and not less: We’d like to see fewer grammatical errors and less pretentious writing. But fewer people know there are exceptions to that rule. If you’re writing about time, money, distance, or weight, the correct word is less, not fewer: less than $100, less than 3 miles, less than 20 pounds, and less than 15 minutes.