In the backoffice, find the settings tab and open up Regional Settings. There you can set the time difference. Since I'm on Eastern Standard, I had to set the time difference to -4.

On your settings tab, regional subtab. Check out the time at the top of your page and add the offset it takes to make it match your current time. You can only do hours, and you can add a negative. Like 3 or -2 or whatever.

What an amazing coincidence of timing this was!

I see we're both quick on the draw. Had to jump at the question - It's not often I'm qualified to answer them on this forum ;)

I just noticed a detail of the original question that needs clarification. The offset isn't against GMT. It is an offset for your server time. So like if your server is 2 or 3 hours away from you then you put in 2 or 3, even if GMT is half way around the world. Anyway both times are on the top of the admin pages so base your offset on your physical time compared to either "blog time" or "time", but not "GMT".