You must still follow all normal timing rules for cards played this way. For example, you may play a land exiled this way only during your main phase and only if you haven't played a land yet this turn.

If Intellect Devourer leaves the battlefield before the Devour Intellect ability resolves, opponents won't exile any cards from their hands.

If a card exiled with the Devour Intellect leaves exile for any reason (most likely because it was played using the Body Thief ability), it won't be returned to the opponent's hand if Intellect Devourer leaves the battlefield.