Ask HN: system which allows messages to be decrypted at a given time?

Could you create a system which allows some encrypted messages to only be decrypted after/at a given time t and without any authority?

There would be so cool applications of such a system, imagine if someone (like Snowden) want to share to the world some important document but which only are auto-decrypted in the future, whatever happen to the person.

Do you think this will ever be possible? I'm afraid this need the time to be provable?