Tutorial available at https://youtu.be/jzYvZkP_vUs

After Effects Dynamic Clock Time and Countdown

// ##################################################
// Tutorial available at https://youtu.be/jzYvZkP_vUs
// ##################################################


	// clock start time HH:MM:SS
	var clockStartAt = "06:00:10";

	//Count Up/ Down rate
	var rate = -1;

	cStr = clockStartAt.split(":");

	// count all seconds for givin time
	var clockStart = (parseInt(cStr[0]) * 3600) + (parseInt(cStr[1]) * 60) + parseInt(cStr[2]);

	// calculate clock time from inPoint of the current text Layer.
	var clockTime = Math.max( clockStart + rate * (time - inPoint), 0);

	var t = Math.floor(clockTime);

	var sec = Math.floor( t % 60 );
	var min = Math.floor( (t % 3600) / 60 );
	var hour = Math.floor( (t % (3600 * 60)) / 3600 );

	// to prefix ZERO, we need to create a function
	function padZero(n){
		if (n < 10 ) return "0"+n else return "" + n;
	}

	// display time with padZero function
	padZero(hour) + ":" + padZero(min) + ":" + padZero(sec);