[Typo3-dev] tt_news date tstamp

[Hallimasch.de]

Hello,

I want to write "by hand" the date of a news into the database. So I created 
with PHP and mktime() a UNIX timestamp and wrote this in the field tstamp in 
tt_news (typo: int(11) ). But the news-plugin shows another date.
So I played around and found out, that

//original date: $std, $min, $sec, $day, $month, $year
$UNIXDate =  mktime($std, $min, $sec, $day, $month, $year );
date("Y-m-d h:i:s", $UNIXDate );

is not giving back the original date.

What do I wrong?
How can I get the integer value for tt_news, that is representing my 
timestamp ($std, $min, $sec, $day, $month, $year)?


Greetings, Hallimasch.de