Temporal clauses are neither restrictive nor nonrestrictive. No comma is needed but if you want to use one, go ahead. There is normally no comma before conjunctions such as
if, when, and
because:I said I would do it if he asked me.
I didn't want to know when he would come.
I asked him because I wanted to know the right answer.
If the sentence is long like yours, a comma may make the meaning clearer in some cases and there is no rule against making one's meaning clearer. It's really up to you. Note that a comma is frequently used if the subordinate clause is before the main clause:
Because I wanted to know the right answer, I asked him.
CB