There's a handy rule of thumb for this: is the number of seconds per minute (60 aka 2*2*3*5) a weird, random-sounding number that's way too easy to make clean subdivisions out of[0], rather than a nice, math-hostile power of ten? Then it's probably already in American units, unless it's British.
0: https://en.wikipedia.org/wiki/Highly_composite_number