PHP Example: Accurate to every second of the number of online display code

<?php
Session_Start ();
$dat _now1=date ("H+i+s");/Take time
$p 2=explode ("+", $dat _now1);
$dat _number1= $p 2[0]*3600+ $p 2[1]*60+ $p 2[2];//take seconds

if ($online _time<> "")//Last Refresh Time
{$dat _h=substr ($online _time,11,2);
$dat _i=substr ($online _time,14,2);
$dat _s=substr ($online _time,17,2);
$dat _number= $dat _h*3600+ $dat _i*60+ $dat _s;
}

$tmptime = $dat _number1-$dat _number;//last to present interval seconds
if (session_is_registered (username) && (($tmptime >300) ¦¦ ($tmptime <0))//if less than 5 minutes
{
$online _time=date ("y-m-d h:i:s");
$STR = "Replace Lt_t_online set lt_username= ' $username ', Lt_lasttime=now ()";//write to Database
$res =mysql_query ($STR);
}
?>
The above files are automatically refreshed once per minute
The following is a 5 minute daemon running
?
$str = "Delete from Lt_t_online where Unix_timestamp (now ())-unix_timestamp (lt_lasttime) >300";
mysql_query ($STR);
?>