[Jess Don]

Hi, I was surfing for a solution to this problem too and I figured out an easier workaround within Premiere Pro CS6:
Just use the offset option of the timecode effect, it’s a frame number so put a negative number of frames you need.

In my case, I need a 2min 30sec countdown so I convert it to frames (30fps in my case) > (2×60+30)x30=4500 frames

Set you desired starting point at 00:00:00:00 with this offset applied and you’ll have the countdown.

You can use the crop effect in order to hide the ‘hours’ or ‘frames’ if you want.
Here a capture:

Hope it helps 🙂