Observe the difference in tense. Foreknown is the perfect participle, has been known from all eternity down to the present “in reference to the place held and continuing to be held by Christ in the divine mind” (Salmond). Manifested is the aorist participle, pointing to a definite act at a given time.
In these last times ( ἐπ' ἐσχάτου τῶν χρόνων)