回复:Please help: I-485 or I-824?
You may file I-824, at any time, when you plan him to apply immigrant visa overseas.
He may also file I-485, while he is present in US, upon your PD being current. Yes, he needs to wait for AP before leaving US, in case he wants to come back after your approval of GC.
http://blog.wenxuecity.com/blogview.php?date=200710&postID=20710#AP