Minutes:Seconds Difference between two dates using UTC

Minutes:Seconds Difference between two dates using UTC

var startDateUtcMilliseconds = "2324324823" // In C#: (buildRun.Date.ToUniversalTime() - new DateTime(1970, 1, 1)).TotalMilliseconds.ToString();
var hours, minutes, seconds;
if (rowItem.currentBuild) {
    var startDate = new Date(parseInt(startDateUtcMilliseconds));
    var msec = Date.now() - startDate;
    hours = Math.floor(msec / 1000 / 60 / 60); // discard
    msec -= hours * 1000 * 60 * 60;
    minutes = Math.floor(msec / 1000 / 60);
    msec -= minutes * 1000 * 60;
    seconds = Math.floor(msec / 1000);
};