afaik negative and broken ints could always lead to problems, so i suggest to use strings.
(afaik it's also the rules of the vb3 coding styles...)
as for the bug, you cannot use float values for mktime iirc, so you would have to use
PHP Code:
$timestamp = mktime (date("H"), date("i") - ($servertime* 60), date("s"), date("m"), date("d"), date("Y"));
instead of
PHP Code:
$timestamp = mktime (date("H")-$servertime, date("i"), date("s"), date("m"), date("d"), date("Y"));