<?php
$string = '> [00:00:00.1] Lorem ipsum dolor sit amet, consectetur adipiscing elit.
> [00:00:02.3] Sed facilisis orci at erat vulputate facilisis.
> [00:00:08.2] Nam aliquam velit quis nisl posuere, ut blandit turpis
> blandit.
> [00:00:13.8] Nulla sit amet metus felis. Nulla aliquam
> ultrices ipsum eget mattis.
> [00:00:19.2] Nulla porta ligula
> scelerisque lorem dapibus porttitor.
> [00:00:26.6] Praesent dolor mi,
> dictum et ante sed, efficitur auctor tortor.
> [00:00:35.5] Praesent
> euismod dui sem,
> vitae pretium nisi suscipit quis.
> [00:00:39.7] Nulla porta ligula scelerisque lorem dapibus porttitor.';
preg_match_all('/\[\K[^\]]+/', $string, $matches);
print_r($matches);