Some fields represent a length of time.
The format of these fields must be: {+|-}hh:mm[:ss] where the leading sign is optional, "hh" represents a number of hours, "mm" represents a number of minutes, and "ss" represents a number of seconds. The "ss" for seconds is optional. If the value is negative, the leading "-" is, of course, mandatory. Leading zeroes for hours and minutes are optional.