I just patched my Redhat AS 3 server with the DST patch and wanted to test it. When I set the date and time with the regular date command :
date 04060259
It did not roll back the time.
When I set the date and time for next Oct :
date 10050159.
It did put forward the time.

I found this explanation :

“Setting the time to 02:59:50 would be ambiguous and the date command takes it to mean the second 02:59:50
that morning rather than the first, and the rollover isn't seen to happen.”

If that is the case. Why did the roll forward work.

Setting it with the UTC time DID work.

date --utc 040515592008.50

date
Sun Apr 6 02:59:50 EST 2008

sleep 20

date
Sun Apr 6 02:00:10 EST 2008

Anyone have any ideas why the time did roll forward but not back
when set with the normal date command and "olson" format
ZONE="Australia/Sydney"

You need to understand why there is an ambiguity.

Assuming DST change at 02:30:00 hrs...
On the roll forward, 02:29:59 changes, next second, to 03:30:00. So there is only one 02:29:50 that day. So there is no ambiguity. (But you just try setting it to 02:50:00!)

On a roll-back, 02:29:59 changes, next second, into... 01:30:00 and all the times from then to 02:29:59 get a second showing. (On the day, 3/4 hour after 1:45 the clock reads 1:30!)

Now, if you set the time within the region, say 0200hrs, then how is the computer supposed to know that you mean before or after DST takes effect?