function explode_time($time) { //explode time and convert into seconds
        $time = explode(':', $time);
	$time = $time[0] * 3600 + $time[1] * 60 + $time[2];
        return $time;
}

function second_to_hhmm($time) { //convert seconds to hh:mm
        $hour 	= floor($time / 3600);
        $minute = strval(floor(($time % 3600) / 60));
		$second  = $time%$minute;

        if ($minute == 0) {
            $minute = "00";
        } else {
            $minute = $minute;
        }
	$time = $hour . ":" . $minute .":". $second;
        return $time;
}

$time = 0;
$time_arr =  array("23:59:10","01:01:10","2:50:00");
 foreach ($time_arr as $time_val) {
    $time +=explode_time($time_val); // this fucntion will convert all hh:mm:ss to seconds
}

echo $time;
echo '<pre>';
echo second_to_hhmm($time);