The minutes (mm) and seconds (ss) are optional. The hour (hh) is required and may be a single digit. The offset following std is required. If no offset follows dst, summer time is assumed to be one hour ahead of standard time. One or more digits may be used; the value is always interpreted as a decimal number. The hour must be between zero and 24, and the minutes (and seconds) — if present — between zero and 59. If preceded by a (‘-’) the time zone shall be east of the Prime Meridian; otherwise it shall be west (which may be indicated by an optional preceding (‘+’)).

where the first date describes when the change from standard to summer time occurs and the second date describes when the change back happens. Each time field describes when, in current local time, the change to the other time is made.

The format of date is one of the following:

J n

The Julian day n (1 ≤ n ≤ 365). Leap days are not counted; that is, in all years — including leap years — February 28 is day 59 and March 1 is day 60. It is impossible to explicitly refer to the occasional February 29.

n

The zero-based Julian day (0 ≤ n ≤ 365 ) . Leap days are counted, and it is possible to refer to February 29.

M m.n.d

The d'th day (0 ≤ d ≤ 6) of week n of month m of the year (1 ≤ n ≤ 5), (1 ≤ m ≤ 12), where week 5 means “the last d day in month m” which may occur in either the fourth or the fifth week). Week 1 is the first week in which the d'th day occurs. Day zero is Sunday.

The time has the same format as offset except that no leading sign (‘-’) or (‘+’) is allowed. The default, if time is not given, is 02:00:00.

If no rule is present in the TZ specification, the rules specified by the tzfile(5)-format file posixrules in the system time conversion information directory are used, with the standard and summer time offsets from UTC replaced by those specified by the offset values in TZ.