What do you mean by a stop watch? A countdown timer, or …? What's this for?
What are you counting down from, and in which timezone? Your users will be visiting your site from all sorts of different locations.
LOL, stopwatch does not needs time zone. It just count down the timer.
Hmm, I did have one bookmarked, but the link is dead now. A quick Google of "jQuery countdown" produces lots of results, though, such as
jQuery Countdown Plugin | jQuery Plugins