Scott Herman writes:
>
> Can anybody tell me what the layout of  the TZTab is?

See below.

> When does EST become EDT? I mean what's the algorithm/rules
> for this? How does TZTab relate to this?

See below.

> Does anybody know of a FAQ for this stuff?

I don't know of a FAQ, but since MPE TZTAB appears to be the same as HPUX
tztab, here's the HPUX man page on the subject:

 tztab(4)                                                           tztab(4)

 NAME
      tztab - time zone adjustment table for date(1) and ctime(3C)

 DESCRIPTION
      The tztab file describes the differences between Coordinated Universal
      Time (UTC) and local time.  Several local areas can be represented
      simultaneously with historical detail.

      The file tztab consists of one or more time zone adjustment entries.
      The first line of the entry contains a unique string that may match
      the value of the TZ string in the user's environment.  The format is
      tznamediffdstzname where tzname is the time zone name or abbreviation,
      diff is the difference in hours from UTC, and dstzname is the name or
      abbreviation of the "Daylight Savings" time zone.  Fractional values
      of diff are expressed in minutes preceded by a colon.  Each such
      string will start with an alphabetic character.

      The second and subsequent lines of each entry details the time zone
      adjustments for that time zone.  The lines contain seven fields each.
      The first six fields specify the first minute in which the time zone
      adjustment, specified in the seventh field, applies.  The fields are
      separated by spaces or tabs.  The first six are integer patterns that
      specify the minute (0-59), hour (0-23), day of the month (1-31), month
      of the year (1-12), year (1970-2038), and day of the week (0-6, with
      0=Sunday).  The minute, hour, and month of the year must contain a
      number in the (respective) range indicated above.  The day of the
      month, year, and day of the week can contain a number as above or two
      numbers separated by a minus (indicating an inclusive range).  Either
      the day of the month or the day of the week field must be a range, the
      other must be simple number.

      The seventh field is a string that describes the time zone adjustment
      in its simplest form: tznamediff where tzname is an alphabetic string
      giving the time zone name or abbreviation, and diff is the difference
      in hours from UTC.  tzname must match either the tzname field or the
      dstzname field in the first line of the time zone adjustment entry.
      Any fractional diff is shown in minutes.

      Comments begin with a # in the first column, and include all
      characters up to a new-line.  Comments are ignored.

      If the value of the TZ string does not match any line in the table, it
      is interpreted according to the current U.S. pattern.

 EXTERNAL INFLUENCES
    International Code Set Support
      Single-byte character code sets are supported.

 EXAMPLES
      The time zone adjustment table for the Eastern Time Zone in the United
      States is:

 Hewlett-Packard Company            - 1 -    HP-UX Release 10.20:  July 1996

 tztab(4)                                                           tztab(4)

           EST5EDT
           0 3 6     1  1974      0-6 EDT4
           0 3 22-28 2  1975      0   EDT4
           0 3 24-30 4  1976-1986 0   EDT4
           0 3 1-7   4  1987-2038 0   EDT4
           0 1 24-30 11 1974      0   EST5
           0 1 25-31 10 1975-2038 0   EST5

      Normally (as indicated in the first line) Eastern Standard Time is
      five hours earlier than UTC.  During Daylight Savings time, it changes
      to a 4 hour difference.  The first time Daylight Savings Time took
      effect (second line) was on January 6, 1974 at 3:00 a.m., EDT.  Note
      that the minute before was 1:59 a.m., EST.  The change back to
      standard time took effect (sixth line) on the last Sunday in November
      of the same year.  At that point, the time went from 1:59 a.m.  EDT to
      1:00 a.m.  EST.  The transition to Daylight Savings Time since then
      has gone from the last Sunday in February (third line) to the last
      Sunday in April (fourth line) to the first Sunday in April (fifth
      line).  The return to standard time for the same period has remained
      at the last Sunday in October (seventh line).

 AUTHOR
      tztab was developed by HP.

 FILES
      /usr/lib/tztab

 SEE ALSO
      date(1), ctime(3C), environ(5).

 Hewlett-Packard Company            - 2 -    HP-UX Release 10.20:  July 1996
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