2Cor3:15 What type of contemproaneity is implied?

Greek Koine and Biblical and Medieval Greek
1

What type of contemporaneity is implied by the use of ἕως and ἡνίκα (ἂν) with the verb κεῖται. I suspect that it is “(longer) period within which” and “for as long as (the action of the main verb lasts)”.

Ἀλλ’ ἕως σήμερον, ἡνίκα ἂν ἀναγινώσκηται Μωϋσῆς, κάλυμμα ἐπὶ τὴν καρδίαν αὐτῶν κεῖται.

What might be the difference between ἕως σήμερον and simply τέως without explication of the σήμερον?

2

How about the contemporaneity or simultaneity expressed by ἄρτι and specifically ἄρτι with a participle? In many cases it seems to be used of pre-existing conditions or circumstances.

Presumably, a comment like, “in later Greek, ἄρτι = νῦν” means that ἄρτι is used where one might have expected νῦν to have been used in earlier texts, because both of them are still used.