An hour from 0 to 23.
int32 hour = 1 [(.max) = { ... }
Minutes of an hour from 0 to 59.
int32 minute = 2 [(.max) = { ... }
Fractions of a second from 0 to 999,999,999.
int32 nano = 4 [(.max) = { ... }
Seconds of a minute, specified from 0 to 59.
int32 second = 3 [(.max) = { ... }