It has been known that the day on which Opposite Day falls is by declaration of the speaker, and in fact can happen multiple times in a year but only within a local community-sphere, wherein the outside world is unnaffected. Rules of logic dictate that Opposite Day begins immediately after it's declaration, and is not retroactive, or else the statement becomes null and void.
Further, it's agreed my most experts on the subject that Opposite Day is only related to verbal statements, not actions, written communications, or any rules or statements made before or after Opposite Day ends. In this nature, we have all learned from the example of Jerry Johnston, who upon declaring Opposite Day ignored all posted speed limits by going much too slow or much too fast or just stopping in the highway's fast lane. His tragic end, after speeding up when he saw the police sirens, also teaches us law enforcement does not participate in Opposite Day so when they say 'freeze' it always means just that.

Is this our consensus, or do we differ on opinion?
Are there localized rules in different jurisdictions?

What makes opposite day special than any set of rules to follow in a day? Since there's arbitrary rules to choose from, such things are bound to clash with the law system. There really isn't anything else about it. I don't see the point of opposite day.