Time represented as an
Int63.t number of nanoseconds since the epoch.
Unix epoch (1970-01-01 00:00:00 UTC)
Will raise on 32-bit platforms. Consider
next_multiple ~base ~after ~interval returns the smallest
time of the form:
time = base + k * interval
k >= 0 and
time > after. It is an error if
interval <= 0.
~can_equal_after:true allows the result to satisfy
time >= after.