Around 2 weeks. However, the trick is in the number of times you keep practicing.
The more you practice, the faster you become.
When you set the maximum number of questions "ex 100" and finish them in one try, the second try will have another 100, but with only 30 new ones. Therefore, in the second time, you would be going through the same thing with only 30 new ones.
Then, you keep repeating the process, and getting like 20 or 30 new ones out of the 100 questions every time you start a new test.
That is how I was going through around 800 a day.
When you check the other sites, they will have almost the same questions but in a different format, which would only confirm that you understand what you are answering.
The new sites will have the same trick. As you set the maximum number every time and finish them all, you get to see bunch of new questions mixed up with the ones you have already gone through.
If you keep repeating the same thing over and over, and score a full mark every time, it means you are ready to beat the actuall 20 questions test with a full mark.
Good luck.