***** NOT A TEACHER *****
I love questions such as yours!
Am I going to answer it? No.
Like you, I am waiting for the answer from someone.
I checked the "books" section of Google (where thousands of books are digitalized for our use), and I noticed that a few writers did use "fewer" in sentences similar to yours. That does NOT mean that they were necessarily correct. After all, many native speakers use incorrect English every day.
I found one passage that I wanted to share with you (all the emphasis is mine):
"During my days in corporate America, I technically lived fewer than 10 miles from my office. Unfortunately, thanks to traffic and congestion, those 10 miles took 90 minutes to drive. That's nine minutes per mile for those keeping score at home." -- Jeff Cohen in his 2008 book The Complete Idiot's Guide to Work Less, Earn More.
Should his use of "fewer" be considered "wrong"? I do not know. Would it be marked "wrong" on a test? Probably.
Is it possible that Mr. Cohen was thinking less of total distance and more of each individual mile? I am just asking.
Interested in Language