Full Idea
Reichenbach wanted to implement a causal theory of time. He did not stipulate that causes are temporally prior to their effects. Instead, he constructs a theory of causal relations to yield a causal asymmetry which is used to define temporal priority.
Gist of Idea
A theory of causal relations yields an asymmetry which defines the direction of time
Source
report of Hans Reichenbach (The Direction of Time [1956]) by Wesley Salmon - Probabilistic Causality
Book Reference
'Causation', ed/tr. Sosa,E. /Tooley,M. [OUP 1993], p.138
A Reaction
I find his approach implausible. I suspect strong empiricism is behind it - that he wants to build from observable causes to unobservable time, not vice versa. But normal intuition sees time as one of the bedrocks of reality, making events possible.