It was a time before I knew you.
In this sentence, the subordinate clause 'before I knew you' acts as an adjectival noun complement to 'time'. 'Before' is not a relative adverb that I am aware of, so what is happening here?
The best explanation I could think of is that there is an omitted object after 'before' (see the example below).
It was a time before the time when I knew you.
By expanding the sentence like this, we can see that 'before' becomes a preposition. The noun 'time' is repeated and modified by the relative clause 'when I knew you'.
Is this an appropriate explanation, or am I completely off track?