You can do a trick where you make a transaction from a private key with a nLockT...

nwh on Dec 4, 2013 | parent | context | favorite | on: Show HN: Bitrated – Bitcoin m-of-n arbitrated tran...

You can do a trick where you make a transaction from a private key with a nLockTime set in the future, then not broadcast it until that date, and destroy the original private hey. Then the only option is to wait until the time or block number set.