Clauses introduced by relative adverbs (or conjunctions) of time, have, in general, the same constructions as clauses introduced by relative pronouns ( cross340, cross2493 ff.) and by relative adverbs of place and manner. Temporal clauses are treated separately for the sake of clearness.
a. Temporal clauses introduced by a word meaning
b. Strictly ὅτε, ἔνθα, ὡς, etc., are subordinating conjunctions when the clause introduced by them fixes the time, place, or manner of the main clause; but are relative adverbs when they serve only to define the antecedent and introduce a clause merely supplementary to the main clause.
Herbert Weir Smyth [n.d.], A Greek Grammar for Colleges; Machine readable text [info] [word count] [Smyth].