I am not sure. I don't see any options but I am EST and it is dead on the money. Someone would have to download in another timezone and see if it is correct. It might be based on where your phone is.
Tried it myself, it appears to be matching the countdown on http://skyrim2011.info/ which at the time of this writing is 2 days 1 hour 56 minutes for me.
I'm GMT+1 and my Steam countdown is 1 hour late due to DST. Looks like it works as intended.