@Greendotz
When they said "you'll know when you start" they really do mean that. If you click on the link it tells you exactly what you need to do, and you can close out of it and get back into it at any time. I waited two days after clicking on the link before even doing the little test. There is even a practice test you can do as much as you like.
All the test is is a "reaction time" test. You're given a series of characters like: "GHJXCZ" and on the right you're given a list of about five or so similar ones, with one out of those five being the same as the one on the left. You have 9 seconds to select it. After each round of 5 questions the time limit drops down to 8 and so on until you only have 5 seconds to answer them.