The distinction between these terms depends on more than whether the noun in question is countable or uncountable.
Q. I recently read a magazine article that contained the phrase less than two weeks ago. That sounds correct, but shouldn’t it actually be fewer than two weeks ago?
A. No, the magazine got it right. Below is a quick summary of the guidelines for fewer and less.
In general, use fewer with nouns that can be counted, and less with nouns that cannot. For instance:
Fewer than 100 consultants attended the conference.
She ordered 40 new computers, even though her boss believed that fewer would suffice.
He lost 20 pounds by putting less sugar in his morning coffee.
I wish there were less parsley in my salad.
There are exceptions, however, to this fewer–less distinction. While it is true that units of time, weight, and distance can be counted (they frequently appear with numbers, after all), when people hear a phrase such as 100 pounds, they tend to think of that weight not in terms of its individual component pounds (one pound, two pounds, three pounds, etc.), but rather, as a single blob or lump of weight. In general, therefore, use less with units of weight; the same principle applies to units of time and distance.
That adult male elephant weighs more than 14,000 pounds, but its baby weighs less than 200 pounds.
The meeting lasted less than 20 minutes.
I ran less than three miles before succumbing to a craving for ice cream.
The phrase you mentioned from the magazine article would work the same way. Less than two weeks ago is describing essentially a lump of time and therefore makes more sense than fewer than two weeks ago.