the problem is strtotime($nowtimecode)
strtotime converts a date string to a timestamp. if it cannot convert it, i beleive it returns -1.
you already have the timestamp so you dont need to use that. this code should work fine>
$servertime = time();
$nowtimecode = $servertime - 7200;
$printtime = date('G i', $nowtimecode);
echo $printtime;