Meta album code is in include/functions.inc.php get_pic_data(). You need to add a restriction based on ctime which is a unix timestamp.
$query = "SELECT COUNT(*) from {$CONFIG['TABLE_PICTURES']} WHERE approved = 'YES' AND votes >= '{$CONFIG['min_votes_for_rating']}' $META_ALBUM_SET";
$result = cpg_db_query($query);
$nbEnr = mysql_fetch_array($result);
$count = $nbEnr[0];
mysql_free_result($result);
//if($select_columns != '*') $select_columns .= ', pic_rating, votes, aid, owner_id, owner_name';
$select_columns = '*'; //allows building any data into any thumbnail caption
$query = "SELECT $select_columns FROM {$CONFIG['TABLE_PICTURES']} WHERE approved = 'YES' AND votes >= '{$CONFIG['min_votes_for_rating']}' $META_ALBUM_SET ORDER BY pic_rating DESC, votes DESC, pid DESC $limit";
$result = cpg_db_query($query);
$rowset = cpg_db_fetch_rowset($result);
mysql_free_result($result);
Becomes something like this
$query = "SELECT COUNT(*) from {$CONFIG['TABLE_PICTURES']} WHERE approved = 'YES' AND votes >= '{$CONFIG['min_votes_for_rating']}' AND ctime > UNIX_TIMESTAMP() - 86400 $META_ALBUM_SET";
$result = cpg_db_query($query);
$nbEnr = mysql_fetch_array($result);
$count = $nbEnr[0];
mysql_free_result($result);
//if($select_columns != '*') $select_columns .= ', pic_rating, votes, aid, owner_id, owner_name';
$select_columns = '*'; //allows building any data into any thumbnail caption
$query = "SELECT $select_columns FROM {$CONFIG['TABLE_PICTURES']} WHERE approved = 'YES' AND votes >= '{$CONFIG['min_votes_for_rating']}' AND ctime > UNIX_TIMESTAMP() - 86400 $META_ALBUM_SET ORDER BY pic_rating DESC, votes DESC, pid DESC $limit";
$result = cpg_db_query($query);
$rowset = cpg_db_fetch_rowset($result);
mysql_free_result($result);
Change 86400 to the number of seconds you want to filter on.