Signed fractions of a second at nanosecond resolution of the span of time. Durations less than one second are represented with a 0 `seconds` field and a positive or negative `nanos` field. For durations of one second or more, a non-zero value for the `nanos` field must be of the same sign as the `seconds` field. Must be from -999,999,999 to +999,999,999 inclusive.