There is a rule about this, the details of which I can't quite remember. Long story short, a subclause of a sentence whose main clause is in the future tense needs to be in the present tense.
X will happen when Y is complete.
If you said
X will happen when Y will be complete.
It would 'sound wrong'. In essence you need to convey the order that things will happen by using different tenses that happen before the final event. You can say either of the following, and they mean the same thing:
X will happen when Y completes.
X will happen when Y has completed.
All the events are in the future, even though the tense in the second part of the sentence is present or present perfect.
Usually you can use any tense at all in subordinate clauses. The use of a conjunction which conveys an order in time (here 'when' and 'until') makes it a little more restrictive.