Welcome and good luck!
Anton Ivanov said:
My goal is to become a member myself this year. As I understand it, a new class should start in July/August (unless I'm reading the instructions wrong and you can start the challenge any time), which I intend to join.
You can start the challenge at any time. Classes are when you apply to become a member after completing the challenge goals. As SB pointed out, you must be in the challenge for at least 6 months (that is one of the goals, along with the Alexa ranking and making connections) before you can be accepted as a member.
So officially join the challenge before the upcoming class date in order to be eligible to apply for membership at the next class, which should be early in next year.