Tweak from my other Gist, https://gist.github.com/betamos/6306412. Outputs seconds into "h+:mm:ss"

readable-duration-so.js

/* Author: Didrik Nordström, didrik@betamos.se */
/* Specifically for http://stackoverflow.com/questions/6312993 */
 
/**
 * Format a duration in seconds to a human readable format using the notion
 * "h+:mm:ss", e.g. "4:40:78". Negative durations are preceeded by "-".
 *
 * @param t Duration in seconds
 * @return The formatted duration string
 */
var readableDuration = (function() {
 
	// Each unit is an object with a suffix s and divisor d
	var units = [
		{s: '', d: 1}, // Seconds
		{s: ':', d: 60}, // Minutes
		{s: ':', d: 60}, // Hours
	];
 
	// Closure function
	return function(t) {
		t = parseInt(t); // In order to use modulus
		var trunc, n = Math.abs(t), i, out = []; // out: list of strings to concat
		for (i = 0; i < units.length; i++) {
			n = Math.floor(n / units[i].d); // Total number of this unit
			// Truncate e.g. 26h to 2h using modulus with next unit divisor
			if (i+1 < units.length) // Tweak substr with two digits
				trunc = ('00'+ n % units[i+1].d).substr(-2, 2); // …if not final unit
			else
				trunc = n;
			out.unshift(''+ trunc + units[i].s); // Output
		}
		(t < 0) ? out.unshift('-') : null; // Handle negative durations
		return out.join('');
	};
})();