This is what I am using:
Milliseconds to a pretty format time string:
function ms2Time(ms) {
var secs = ms / 1000;
ms = Math.floor(ms % 1000);
var minutes = secs / 60;
secs = Math.floor(secs % 60);
var hours = minutes / 60;
minutes = Math.floor(minutes % 60);
hours = Math.floor(hours % 24);
return hours + ":" + minutes + ":" + secs + "." + ms;
}