In reply to Justin Tadlock.

Website owner can adjust time by increasing or descreasing complexity in the settings. And by "almost" I meant that speed of unlocking is not very much depending on download speed, but still does, since it need to download javascript, images and styles to show it off. After that - it is only browser and computer speed what does matter.

As time will go and computers and browsers become faster, it will be matter of adjusting complexity to keep up with it.

Right now default suggested complexity is 0.01, which translates on modern computer and browser to about 5-10 seconds of unlock time. I believe lowest value you can go and still be practical is 0.001, after that it is gets too easy to protect against anything.