I see you managed to confuse a number of people there. :)
Long answer: no issue because both time() function in PHP and unix_timestamp() function in MySQL reference the same value: seconds since 00:00:00 UTC January 1, 1970 (disregarding leap seconds). Using unix_timestamp()+13*60*60 will be exactly 13 hours from now, regardless of what the local timezone is where you read that statement and regardless of the delta of your local timezones.
Local timezone is a relative measure, POSIX time (or Unix time or Unix epoch) is absolute.