FYI this stuff is implemented by the Automatic DST mod
for phpBB3, the software that this forum is based on. It's not code that I wrote, but I chose to install it because the default phpBB behavior is not
automatic -- if your region has daylight savings time, then you had to tell the forum, twice a year, whether DST is in effect or not. There was a check box in your Board preferences for that, which is now gone with this mod.
In order to provide automatic DST changes, the timezone selection cannot simply be UTC +/- some offset, because that does not provide any info whether a specific location within that timezone implements DST, and when does DST go in and out of effect. Thus the author of the mod chose a city-based menu. The logic behind it is described by the author in the following post:http://www.phpbb.com/community/viewtopic.php?f=70&t=1496415&start=15#p8941785
I do agree that the current menu is rather sparse. But upon doing a little checking I found that you could select "America/Indiana/Knox" and it will give you what you need (there may be others that would work too).
Here is an interactive timezone map of the world:http://www.timeanddate.com/time/map/
At that site, you can click on a city in your local timezone and go to the Time/General page for that city. You can see whether that city has the same time as yours. Then, click on the Time Zone and DST tabs to see if they match what your local rules are. When in doubt, you can search your city (or another major city closer to you) in the search box and compare.
Sorry that it has to be so complicated, but timezones and DST are a messy issue with many different geopolitical rules. I installed this mod so that you can set it once and forget it (even though it might take a little more initial work), but thereafter the system will take care of DST changes and display the correct time automatically.