Let me add a remark about CPT theorem and its possible applications - most physicists believe this symmetry is satisfied, it also contains time symmetry. So can we prove that causality only works past -> future? (as in Euler-Lagrange, in contrast to the least action principle).

For example laser causes excitation of target later - so shouldn't CPT analogue of laser cause deexcitation of target earlier?

While building "CPT analogue of laser" might seem extremely difficult, for free electron laser (FEL) it looks quite simple:

I was listening to the working session on April 30th, and Stephen seemed to be saying that Time is special, and the idea of a block future universe (where the future is "calculated" in advance) can't happen because of computational irreducibility.

Did I misunderstand the discussion?

An interesting and subtle question!

Of course, our model is only deterministic up to measurement. As detailed in my quantum mechanics paper (https://www.wolframphysics.org/technical-documents/) different choices of quantum observation frame, corresponding to different choices of measurement sequence, generally distinct causal graphs (in much the same way as different foliation choices in the causal graph generally yield distinct spatial hypergraphs). So I'd argue that our model implies a refinement of the block universe concept, in which it is not spacetime (i.e the causal graph), but rather branchtime (i.e. the multiway causal graph), that is the invariant structure containing all past, present and future events.