$w = DB_DataObject::factory($this->table);
$w->whereAdd('act_when > sent'); // eg.. sent is not valid..
+ $w->whereAdd('act_when > NOW()'); // eg.. not if future..
+
$w->orderBy('act_when ASC'); // oldest first.
$w->limit(1000); // we can run 1000 ...
$ar = $w->fetchAll('id');