Need help modifying something

[gingery]

I'm trying to modify this code from a "top posters" plugin:

$rows = 10;
$query="select * from " . TABLE_PREFIX . "user ORDER BY posts desc limit $rows";
$rt=mysql_query($query);
echo mysql_error();


while($nt=mysql_fetch_array($rt)){
$test .= "<a href='member.php?u=$nt[userid]'>$nt[username]</a> ($nt[posts]),  ";
}

to show the top posters for the last 24 hours instead of the top posters of all time. I've played around with it a bit but really have no clue as to what I need to do. I'm sure it is an easy fix for someone who knows how to code. Can anyone help me?