time difference between forum database and time()

[bosal]

Hello.

I want to make simple script in PHP, that will check, if latest thread in specified board is older than 7 days, and if so, random thread from different board will be moved to that board. I just have small problem about it, because i don't what time difference is between time() and dateline in database.

Here's what i'm doing:

PHP Code:

     $tsql = mysql_query("SELECT threadid,title,dateline FROM thread WHERE forumid=$poll_forum_id and open=1 ORDER BY dateline DESC LIMIT 1");
     $temat=mysql_fetch_array($tsql);
     
     $timediff=2*60*60-7; // it looks like around 2 hours, but not exactly, i have no idea what this value should be.
     
     if ($temat['dateline']+$timediff<time()-7*24*60*60) // is thread older than 7 days
     {
        $tsql = mysql_query("SELECT threadid FROM thread WHERE forumid=158 and open=1 ORDER BY rand() LIMIT 1");
        if (mysql_num_rows($tsql)>0)
        {
           $th=mysql_fetch_array($tsql);
           mysql_query('UPDATE `thread` SET (
              forumid='.$poll_forum_id.',
              dateline='.now()+$timediff .') where threadid='.$th['threadid']);
        }
     } 


For me this difference looks like something around 2 hours, but not exactly, few secounds less. How can i get this difference and be sure, than when time will be changed from summer to winter it will still work fine?