show remaining seconds every day PHP

I am trying to create a script showing the missing seconds for 10am on 'CEST' time. The problem is when it is for example 10:01, negative seconds are displayed. I clarify that it is for each day, regardless of date. I hope you can help me

<?php
date_default_timezone_set('Europe/Berlin');
$inicio = new DateTime('10:00:00');
$HoraActual = date("H:i:s");
$hr = new DateTime($HoraActual);
$tiempo = $inicio->diff($hr);

$diff = $inicio->getTimestamp() - $hr->getTimestamp();
print $diff

?>