I present this small service to your court - TellYouLater.com . The service is only a few months old, but he already knows how to encrypt the message in such a way that no one can read it until a given point in time. Actually, only this service is able.
Here is an example of a self-decrypting message: http://goo.gl/YdIzI (QR next to it).

Algorithms

This area of ​​cryptography in English is called Time-Lapse Cryptography and is so modern that it has not even acquired a Wikipedia page.
The service uses the simplest Time-Lapse Cryptography scheme: for every hour in the next few years a pair of keys has been created - public and secret. All public keys are available, and secret keys are published only at the appropriate time.
The server’s duty is only to publish secret and public keys, and encryption / decryption is performed on the client side (of course, this is JavaScript). That is, the message will not get into the network without the user's knowledge.
The implementation of 1024-bit RSA and 128-bit AES in JavaScript is optimized quite well (including thanks to the Google Closure Compiler) and is performed instantly on most devices. It was necessary, however, to tinker with IE, which suggested the user to interrupt the script (although the script worked for less than a second).

Infrastructure

The web server is kindly provided by a young but promising provider , with the ridiculous name Guugl.
The website itself does not store secret keys, the site requests them from the intermediate storage somewhere on the Internet. Very different servers keep secret keys (each server knows only its own part of the key), and they publish them at a specified time in this very repository.
Keys generated by the OpenPGP program.
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Conclusion

The scope of this service is vast - from ... well, I do not know, until ... you need to think.
In general, use on health.

PS I’m clarifying that the original and encrypted messages are not transmitted to the server, are not stored or distributed. What to do with the encrypted message is decided by the user. The server processes only the requests “Give secret / public key at such and such hour”. The rest is JavaScript on the client.