how to start timing or stop watch at 15 sec?

I am using below script to start the timing. (Click on source text and paste the below script). But it is automatically starting timing from 0. I want that timing should start from 15 sec. How to do that?

rate = 1;

clockStart = 15;

function padZero(n){

if (n < 10) return "0" + n else return "" + n

}

clockTime = Math.max(clockStart + rate*(time - inPoint),0);

t = Math.floor(clockTime);

min = Math.floor((t%3600)/60);

sec = Math.floor(t%60);

min + ":" + padZero(sec)