For instance, this works just fine and produces a reasonable answer:
(2577 miles / (speed of light)) in milliseconds ==> 13.83 ms
But this fails, with the question being interpreted incorrectly:
((distance from SF to NY) / (speed of light)) in milliseconds ==> [?] distance from San Francisco to New York -> Quantity[2577, "Miles"]
Is there a different way to ask this question that should work?
Well, after further research, I've found this this approach (though unintuitive) works:
(distance from SF to NY in meters) / (speed of light in meters per millisecond) ==> 13.83 ms