Duration template specializations like Seconds affect the precision of operations. E.g. Seconds(1) / 2 results in a zero-duration object. I had been belaboring under the assumption that the template specializations are a syntactical convenience so that e.g. Milliseconds(86400000) can be written as Days(1). I think it's unintuitive for the duration subtype to have an effect on arithmetic precision.

Change the duration types so that arithmetic operations use a common, reasonably fine-grained precision.