It should not matter though, because std::chrono is not int-convertible - so is it "milliseconds" or "microseconds" or whatever is an minor implementation detai

It should not matter though, because std::chrono is not int-convertible - so is it "milliseconds" or "microseconds" or whatever is an minor implementation detail. You cannot compile FooBar(5000), so there is never confusion in C++ like C has. You have to do explicit "FooBar(std::chrono::milliseconds(500))" or "FooBar(500ms)" if you have literals enabled. And this will handle conversion if needed - you can always do FooBar(500ms) and it will work even if actual type in microseconds. Similarly, your "auto" example will only compile if gl_timeout is a compatible type, so you don't have to worry about units at all when all your intervals are using std::chrono.