As far as I can tell the website provides no way to revoke or otherwise hide a prediction once you make it - it will always be revealed at the specified date.
Additionally, the creation screen proclaims:
> There is no way to edit or delete a pok after you save it
Could hack this system by holding two accounts, each one making predictions in opposite directions, then burn the one that was wrong. This would work for the first prediction, but becomes geometrically more difficult to manage fabricating a history of correct predictions.
They would need to implement a feature where others can see that someone has made a prediction, and a maximum time for how long the prediction can stay hidden.
EDIT: That is exactly how it works. They write " There is no way to edit or delete a pok after you save it".
Additionally, the creation screen proclaims:
> There is no way to edit or delete a pok after you save it