The elect were in Christ by election before the foundation when God loved them from Eph 1:4
4 According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:
Gods Love is only in Christ Jesus Rom 8:39
39 Nor height, nor depth, nor any other creature, shall be able to separate us from the love of God, which is in Christ Jesus our Lord.
The love of God here has the definite article, so its definite only in Christ Jesus,
ὔτε ὕψωμα οὔτε βάθος οὔτε τις κτίσις ἑτέρα δυνήσεται ἡμᾶς χωρίσαι ἀπὸ τῆς ἀγάπης τοῦ θεοῦ τῆς ἐν Χριστῷ Ἰησοῦ τῷ κυρίῳ ἡμῶν
You cant be outside of Christ Jesus and be Loved by God. Gods Love began in the Eternal Phase of Salvation where also did Unconditional election
Eph 1:13 and Rom 16:7 are about the Spiritual phase of Salvation
See in the Eternal Phase of Salvation, all the elect members were all at once chosen in Christ Eph 1:4
However they dont all come into the world at the same time, some were born in the 1700s, some in the 1800s and etc, and they experience the Spiritual phase during their generation. So if one elect is converted 1723 and one was born and converted in 1823 , the one born in 1723 was converted in Christ Spiritually before the one who was born in 1823
All the elect are not born again individually at the same time. Peter was in Christ Spiritually before Paul but when in the eternal phase they were in Christ by election at the same time.