I added CCleaner due to the recommendation in the book WikiLeaks by The Guradian's Leigh and Harding, that all who communicate using the interned have access to and use Secure Socket Layer, Pretty Good Privacy, The Onion router Net and a DRIVE WIPER. No, you won't find all that 'recommendation' in one paragraph, but ... read the book.
How long should it take to wipe free space? Yes, a complicated answer is implied by various file systems, disk speeds, processor speed and file arrangement. How long is a reasonable time to wait?
Thanks to all that help. God save the Japanese and the Fukushima NPP workers.
As you have already insinuated knowing WFS takes as long as it needs to do the free space (if you have 1mb of free space it's quick, if you have 300GB of free space and much of that space was once used space it'll take a looooong time)
That said, WFS is a drive destroying process if done too much (or even too many passes). Yes it'll make it harder for a recovery program to recover anything useful. But if you are worried about big brother getting your wikileaks data, I'd not count on anything apart from running a drill press (as in the Wood shop tool) through the drive.
That said, if you want to know your just gonna have to let it finish, there are just too many variables (including the phase of the moon ) to give even an estimate for how long wfs would take.