3v4l.org

run code in 300+ PHP versions simultaneously
<?php $start=strtotime('00:00'); $end=strtotime('23:30'); for ($halfhour='00:00';$halfhour<='23:30';$halfhour=$halfhour+30*60) { printf('<option value="%s">%s</option>',date('H:i',$halfhour),date('g:i a',$halfhour)); } ?>

preferences:
42.56 ms | 402 KiB | 5 Q