Let's do the Time Warp again!
By Mike Dietrich-Oracle on Jun 20, 2012
Once you start reading about Daylight Saving Time changes in MyOracleSupport you'll find still a lot of notes explaining this and that and back and forth. But sometimes there seems to be a bit too much information - and lacking clear instructions. Once a customer called that the "Time Zone Spaghetti" after reading MOS notes about DST for several hours ending up with the note where he has begun to read before still not clear what to do now
I'm using usually the scripts from MOS Note:977512.1 as you'll just have to exchange the DST version you are upgrading to and it has everything you need to check and adjust the time zone data in the database - for instance after applying the DST V18 patch to your database's homes. As a reminder to myself when traveling I have stored a copy of the script part of that note here - and please note that this is not an official Oracle version. Always read and check the original MOS Note:977512.1 as it may have gotten changed in between and may contain changes or corrections and as it has a lot of more explainationary information than I could cover here.
And credit to Gunter Vermeir from Oracle Support, who is the owner of that MOS Note and has compiled all that useful stuff together.