I remember an argument about quantum uncertainty being the "out" for freedom of choice. Although the universe appears to be deterministic, quantum probabilities mean the universe evolves statistically in a local-time sense, albeit its global structure now could also be said to have a history which is fixed, thus determined at the BB. Hawking said something like the apparent fixed past is actually us creating a particular history out of the probabilities (also present since particles appeared). The universe and determinism are weirder than we thought. Or to paraphrase, we have the freedom to choose a past by measuring quantum states "from" the past, this is the conjectured invariant which is true "in or at" every now (is true locally and globally). As for any "now" we have only quantum uncertainty, so we can only create a past and assert that it's fixed.