increment-time.php

<?php
/**
 * Soma um ou mais horários no formato 00:00
 *
 * @link https://vijayasankarn.wordpress.com/2016/12/27/sum-n-times-php/ 
 *
 * @param array $times Lista de horários para somar
 * @return string
 */
function increment_time(array $times)
{
    
    $seconds = 0;
    foreach ($times as $time) {
        list($hour, $minute, $second) = array_pad(explode(':', $time), 3, null);
        $seconds += $hour * 3600;
        $seconds += $minute * 60;
        $seconds += $second;
    }
    $hours = floor($seconds / 3600);
    $seconds -= $hours * 3600;
    $minutes  = floor($seconds / 60);
    $seconds -= $minutes * 60;

    return sprintf('%02d:%02d:%02d', $hours, $minutes, $seconds);

}