Arkansas (Central Standard Time) is GMT -6 (minus six).
Because it works out to exactly 12 hours difference if you select +6 instead, the time will look right, but the date will be wrong, as you will have set your timezone for the opposite side of the world.
I did notice a few people have it set that way.
Also, to adjust for Daylight Savings Time, you can set it to GMT-5 insted of -6. Just remember to set it back to -6 when we go from CTD to CST.
I wish Nuke/phpBB (the software running the site) would just automatically adjust for DST, but I don't think it can.