// 회원테이블 연결
$sql = " select * from $g4[member_table] where mb_today_login >= '$str_today_time' order by mb_today_login asc, mb_point asc ";    <-- 이부분을 수정하시면 될것 같네요.
$result = sql_query($sql);

5등급 이상만 출력 한다면

$sql = " select * from $g4[member_table] where mb_today_login >= '$str_today_time' and mb_level >= 5 order by mb_today_login asc, mb_point asc ";