Hmm, my testing has been a bit bad... It should take about 5-30 seconds, depending on your machine.
It uses a web worker to do the calculations, so it shouldn't hang until it starts plotting stuff.
What OS + browser are you using? I noticed that it doesn't work on Opera, for example. But on chrome it works decently even on my phone.
Most of the calculations are done client-side, the server-side calculations only take a few seconds.
