time counter with user input as start

gistfile1.php

list($hours, $minutes, $seconds) = explode(':', $_POST['time']);

$seconds = $hours * 3600 + $minutes * 60 + $seconds;

for ($i = $seconds; $i > 0; $i--)
{
   echo $i;
   sleep(1);
   flush();
}

echo 'Countdown finished.';