is Cool does Real
Duration represents a length of time in atomic seconds, with fractions. Like an Instant, it is epoch-agnostic.
Durations can be subtracted from or added to
Instants to yield another, new
Instant. Subtracting one
Instant from another yields a
Duration can also result from mathematical operations between two
Durations when it makes sense (namely, the addition, subtraction, or modulus of two
Durations). It can also be added, subtracted or divided modulo Real numbers.
The type of object returned for other numeric operations is currently unspecified.