The future indicative is rarely used in temporal clauses; and when used refers to definite time.
τηνικαῦτα . . . ὅτε οὐδ' ὅ τι χρὴ ποιεῖν ἕξετε
a. The future is rare because that tense does not usually make clear the difference between action continuing and action simply occurring in the future. ὅτε with the future indicative has thus been almost entirely displaced by ὅταν with the subjunctive.
b. For the future with κέ in θ 318 the subjunctive is probably correct.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].