I do believe you have considerable time to register the public key. My understanding is that you can claim your tokens anytime after the window for investing closes, meaning you could wait the 341 day period, and probably for a brief period after that. I also think you can wait that long to register your key. Your public key must be registered before the EOS guys take a snapshot of all registered public keys from the Ethereum blockchain to build the genesis block of the EOS blockchain. Some people are wagering they can participate and figure out these details later, and I agree someone will probably make an easier tutorial during that period. But please be aware this understanding I have is not guaranteed, it is just my best guess from how the documentation is written and my technical understanding. It would be better to see something the EOS guys have provided on this about deadlines to do these activities.