When do other states usually begin contraflow?
Contraflow is not a time "when". When the first response is in place, and when the resources are deployed, then contraflow happens in Texas. Other states have very different conditions.
Re when to start 'contraflow' - I don't think there is a 'usual' timeline established. But I should guess that if you tell people that the MANDATORY evac will start at 6am, you start the contraflow a bit earlier than that, so that the voluntary evacuees who leave early (like 3-4am?) will have a route out.
We're all learning, I hope. But because it is so difficult I hesitate to blame anyone...