IBM says:

Changing the Effective Date to Switch to DST
=================================
If you wish to change the date or time at which the system switches to DST
and back to ST, edit the TZ line in /etc/environment.
Change the line to read like the following:

   TZ=CST6CDT,M4.1.0/1:00:00,M10.1.0/1:00:00

This would effect a change to Daylight Savings Time at 1:00 AM on the first
Sunday in April and change back at 1:00 AM on the first Sunday in October,
and keep the US Central Time Zone time offset from GMT. The breakdown of the
string is

*CST6CDT is the time zone you are in; *M4 is the fourth month; *.1 is the
first occurrence of a day in the month; *.0 is Sunday; */1:00:00 is the
time.

In more detail the format is TZ = local_timezone,date/time,date/time. Here
date is in the form of Mm.n.d, day d(0-6) of week n (1-5, where week 5 means
"the last d day in month m" and which may occur in either the fourth or the
fifth week) of month m of the year. Week 1 is the first week in which the
day d occurs. Day zero is Sunday. This format is compliant with POSIX 1003.1
standards for Extensions to Time Functions.

Note: If you are running AIX version 4.1 and the fileset bos.sysmgt.smit is
at 4.1.5.6 or greater, you can change this in the chtz smit panel.

If you are running AIX version 4.2 and the fileset bos.sysmgt.smit is at
4.2.1.4 or greater you can change this in the chtz smit panel.

AIX version 4.3 supports changing this in the chtz smit panel by default.

Hope this helps.
S. Wolf
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EMail:  [mailto:S.Wolf AT hzd.hessen DOT de]
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