[Chadi]

How do I edit the timezone?

Members who have visited (2) shows this (plugin)

if ($show['wvt'])
{
	if ($vbulletin->options['wvt24'])
	{
		$cutoff = TIMENOW - 86400;
		$whodesc = $vbphrase['visited_today_24'];
	}
	else
	{
		$whodesc = $vbphrase['visited_today'];
		$tnow = date('YmdHis',TIMENOW - intval($vbulletin->options['hourdiff'])); 
		$cutoff = TIMENOW - (substr($tnow,8,2)*3600 + substr($tnow,10,2)*60 + substr($tnow,12,2)); 
	}

	$todaysusers = $vbulletin->db->query_read("
		SELECT userid, lastactivity, options, username, user.usergroupid, displaygroupid, 
		groupa.opentag as opentaga, groupa.closetag as closetaga, 
		groupb.opentag as opentagb, groupb.closetag as closetagb
		FROM " . TABLE_PREFIX . "user as user
		LEFT JOIN " . TABLE_PREFIX . "usergroup as groupa ON(user.usergroupid = groupa.usergroupid)
		LEFT JOIN " . TABLE_PREFIX . "usergroup as groupb ON(user.displaygroupid = groupb.usergroupid)
		WHERE lastactivity > " .$cutoff. " ORDER BY username
	"); 
		
	$totaltoday = 0;
	unset ($whotoday);
	while ($today = $vbulletin->db->fetch_array($todaysusers))
	{
		$totaltoday += 1;
		$today['opentag'] = $today['opentaga'] ;
		$today['closetag'] = $today['closetaga'] ;
		if ($today['displaygroupid']) 
		{
			$today['opentag'] = $today['opentagb'] ;
			$today['closetag'] = $today['closetagb'] ;
		}
		$today[visible] = 1 ;
		if ($today['options'] & $vbulletin->bf_misc_useroptions['invisible']) 
		{
			$today['visible'] = 0 ;
			if (($vbulletin->userinfo['permissions']['genericpermissions'] 
			& $vbulletin->bf_ugp_genericpermissions['canseehidden']) 
			OR $today['userid'] == $vbulletin->userinfo['userid'])
			{
				$today['visible'] = 2 ;
			}
		}
		if ($today['visible']) 
		{
			$wrdate = vbdate($vbulletin->options['timeformat'], $today['lastactivity']);
			$whotoday .= "<a href='member.php?u=$today[userid]' title='$wrdate' >";
			if ($today['visible'] == 2) 
			{
				$whotoday .= $today['opentag'].$today['username'].$today['closetag']."</a>*, ";
			}
			else 
			{
				$whotoday .= $today['opentag'].$today['username'].$today['closetag']."</a>, ";
			}
		}
	}
	if ($whotoday)
	{
		$whotoday = substr($whotoday, 0, strlen($whotoday)-2);
	}
	else
	{
		$whotoday = $vbphrase['no_visitors'];
	}
	$search_text = '<!-- end logged-in users -->';
	$vbulletin->templatecache['FORUMHOME'] = str_replace($search_text,
	$search_text.fetch_template('Display_Visitors'),$vbulletin->templatecache['FORUMHOME']);
}

I want the timezone to be Central US (GMT -4:00 if I'm not mistaken). Actually, I would rather
have it "last 24 hrs" if possible without clearing out the list of visited members on the 24th hour