Edit in JSFiddle

function dailyMissionTimer(duration) {
    
    var timer = duration * 3600;
    var hours, minutes, seconds;
    
    var interval = setInterval(function(){
        hours	= parseInt(timer / 3600, 10);
        minutes = parseInt(timer / 60 % 60, 10);
        seconds = parseInt(timer % 60, 10);
		
        hours 	= hours < 10 ? "0" + hours : hours;
        minutes = minutes < 10 ? "0" + minutes : minutes;
        seconds = seconds < 10 ? "0" + seconds : seconds;
		
        $('#time-hour').text(hours);
        $('#time-min').text(minutes);
        $('#time-sec').text(seconds);

        if (--timer < 0) {
            timer = 0;
            clearInterval(interval);
        }
    }, 1000);
}

dailyMissionTimer(24);	// hour base

<span id="time-hour"></span>
<span id="time-min"></span>
<span id="time-sec"></span>