Well, it will take more than a few days, because you need to become a Jr. Member first, to join the campaign. For that, you need 30 activity points. Every 2 weeks you can generate 14 activity in total.
After one week my activity was 28. It took two more weeks to be 42, which was yesterday. Total 21 days minimum to be Jr. Member if you post enough.
Well it is possible, because you have registered on Tuesday before anouncing next week, which was done at the same day but after your registration. It means that the first week of yours lasted couple of hours