Provably fair unknown event time for Bitcoin gambling
You could leverage the blockchain itself and use something based on the hash of the current block. For example, the block hash will end in a 0 bit roughly half the time. It will end in 00 bits roughly 25% of the time, etc. This is exactly the same idea as the bitcoin "difficulty" parameter, you would be using the hashes as a roughly constant rate stream of unpredictable random bits.

I think everybody who participates would agree that the block hashes are not predictable in advance.