Add duration strings into DateInterval

durations.php

<?php

$durations = [
    '2:01:05',
    '2:35:25',
    '1:45:01',
];

function getDateIntervalFromString($duration) {
    $i = 0;
    $totalSeconds = array_reduce(
        array_reverse(explode(':', $duration)),
        function ($prev, $time) use (&$i) {
            if ($prev === null) {
                return (int) $time;
            }
            $i++;
            return $prev + (pow(60, $i) * (int) $time);
        }
    );

    return DateInterval::createFromDateString("{$totalSeconds} seconds");
}

$startTime = new DateTimeImmutable();

$endTime = array_reduce(
    $durations,
    function ($prev, $item) {
        return $prev->add(getDateIntervalFromString($item));
    },
    $startTime
);

echo $startTime
    ->diff($endTime)
    ->format('%H:%I:%S');