Get duration function

This function calculates the time a script executes and returns a string which can be used in the final alert like so:

Here is the code:

var startTime = new Date();
// Do something
var endTime = new Date();
var duration = GetDuration(startTime, endTime);
alert("Finished.\n(time elapsed: " + duration + ")");

function GetDuration(startTime, endTime) {
	var str;
	var duration = (endTime - startTime)/1000;
	duration = Math.round(duration);
	if (duration >= 60) {
		var minutes = Math.floor(duration/60);
		var seconds = duration - (minutes * 60);
		str = minutes + ((minutes != 1) ? " minutes, " :  " minute, ") + seconds + ((seconds != 1) ? " seconds" : " second");
		if (minutes >= 60) {
			var hours = Math.floor(minutes/60);
			minutes = minutes - (hours * 60);
			str = hours + ((hours != 1) ? " hours, " : " hour, ") + minutes + ((minutes != 1) ? " minutes, " :  " minute, ") + seconds + ((seconds != 1) ? " seconds" : " second");
		}
	}
	else {
		str = duration + ((duration != 1) ? " seconds" : " second");
	}

	return str;
}