Tutoring signups open randomly when the queue starts to diminish. The three weeks has to do with the suggested length of a tutoring session, but tutors are allowed to go over or under depending on how much work they think they need with their tutees. Signups usually only remain open for less than a day, due to the popularity of the program. Usually we see 50+ people sign up in that amount of time! I know it sounds tough to get into, but it's really the only way we can do signups without being unfair to different timezones. Good luck getting in, and until then, feel free to read my "Phil's Protips" articles in The Smog. I decided to start that column to help users like yourself who were interested in joining the program but were having a tough time getting in. See ya.