Herbert Weir Smyth, A Greek Grammar for Colleges

a. The addition of ἄν produces the forms ὅταν, ὁπόταν; ἐπά_ν, ἐπήν (both rare in Attic), ἐπειδα?́ν. ἕως ἄν, μέχρι ἄν, ἔστ᾽ ἄν mean as long as or until. ὡς when scarcely ever takes ἄν (for ὡς ἄν while ἕως ἄν is read in S. Aj. 1117, Ph. 1330).

b. The temporal conjunctions have here, in general, the same constructions as conditional ἐά_ν or εἰ. Thus ὁπόταν ῀ ἐά_ν ποτε, ὁπότε ῀ εἴ ποτε.