The 72 hour window means that it takes 72 hours for the transaction to process. During the transfer, the funds are no longer reported in your savings balance or in your normal balance, but you can cancel the withdraw request at any time to return it to the savings balance.

So if on Monday at Noon you initiate a withdraw, Thursday at noon the funds will appear in your normal balance and be available for transfer/spending/powerup/etc.

And it's called a hard fork because the witnesses are actually creating a fork of the network, invalidating the old network. The witnesses get the final say on whether the fork is accepted or not. I don't know if that makes it make any more sense, but I'm still pre-coffee :)