As a general rule, temporal clauses will only occur in the subjunctive if they stand in oratio obliqua, or when
they express more than pure temporal relations.
Dum, for example, will take the subjunctive when meaning ‘as long as’, ‘provided that’ (and thus express a
conditional notion). When meaning ‘until’ (also for donec, quoad) the indicative is used in general, unless a
final sense is expressed.