Use the facility already available in PremPro to make a customised Countdown leader and use motion ( scale / position)to set it where you want in the frame.
You can composite it many ways with the tools available.
I made an ID board with a countdown leader, grey scale & bars that I use for all my broadcast masters.
Craig
Shooter Film Company
Auckland
New Zealand
(Premiere Pro 1.5 / Matrox TRX100 XTreme Pro)