time difference

<!DOCTYPE html>
<html>
<body>

<?php
date_default_timezone_set("America/New_York");

//time from qr code
$qrtime = "11/13/2021 05:16:04am";
$parseqrtime = date_create_from_format("m/d/Y H:i:sa", $qrtime);
echo "QR time:<br>" . date_format($parseqrtime,"m/d/Y H:i:sa"). "<br>";
$qrunix = strtotime(date_format($parseqrtime,"m/d/Y H:i:sa"));
echo "QR Unix:<br>" . $qrunix . "<br>";

$signintime = date("m/d/Y H:i:sa");
echo "Sign in (now) time:<br>" . $signintime . "<br>";
$signinunix = strtotime($signintime);
echo "Sign in Unix:<br>" . $signinunix . "<br>";


$timediff = $signinunix - $qrunix;

echo "Unix subtract: <br>" . $timediff . "<br/>";


?>

</body>
</html>