As background to my question, please note that the English translators generally seem to ignore the word οὗ and leave it untranslated, as we see in the NASB20. However, if I'm understanding BDAG correctly, he uses this specific instance as an example of where this pronoun can be used with ἄχρι as "until the time when."[Romans 11:25 MGNT] (25) οὐ γὰρ θέλω ὑμᾶς ἀγνοεῖν ἀδελφοί τὸ μυστήριον τοῦτο ἵνα μὴ ἦτε παρ᾽ ἑαυτοῖς φρόνιμοι ὅτι πώρωσις ἀπὸ μέρους τῷ Ἰσραὴλ γέγονεν ἄχρις οὗ τὸ πλήρωμα τῶν ἐθνῶν εἰσέλθῃ
[Romans 11:25 NASB20] (25) For I do not want you, brothers [and sisters,] to be uninformed of this mystery--so that you will not be wise in your own estimation--that a partial hardening has happened to Israel until the fullness of the Gentiles has come in;
εἰσέλθῃ is an Aorist Active Subjunctive, so I'm not sure how it works with ingressives. Is it, or might it be an ingressive?...as soon as, after 8, 1, 4.—ἀφʼ οὗ (s. ἀπό 2bγ) when once, since Lk 13:25; 24:21; Rv 16:18. ἄχρι οὗ (s. ἄχρι 1bα) until (the time when) Ac 7:18; Ro 11:25; 1 Cor 11:26; Gal 3:19. Also ἕως οὗ until Mt 1:25; 13:33; 14:22; 17:9; Lk 13:21; D 11:6 al. μέχρις οὗ until Mk 13:30; Gal 4:19.—On the gen. οὗ as an adv. of place s. it as a separate entry...
Arndt, W., Danker, F. W., Bauer, W., & Gingrich, F. W. (2000). A Greek-English lexicon of the New Testament and other early Christian literature (3rd ed., p. 727). Chicago: University of Chicago Press.
More background... as generally translated, the temporary partial judicial hardening of the Jews would persist until the time when gentiles would no longer be converted, and then the hardening would be lifted. I'm shaking the passage to see what else drops out.