Suppose A and B to be simultaneous events happening at time t.
If C imples A that implies B (C -> A -> B) then no time passes from A to B because both arise at the same time. It follows that C -> A -> B is indistinguishible from C -> B -> A, or from C -> A and C -> B. Therefore, it is not possible to infer causality on two simultaneous events, or, put another way, to infer causality is to implicitly state dt > 0 between any two events.