I understand the need for pre-roll ads before web videos. I know we'll need more of them as we move forward.
But the timer on the video player should play down, not up, while the ad runs. Knowing the length of the delay makes it far more bearable to our brains that to watch a running tally of how long the delay has been.
I suspect a test with each style of timer would result in a dramatic difference in bounce rates.
Make your site a pleasant experience in every way possible.