You only get the invite if you end up in the top 8 so you will have to join the next two tournaments and get enough points to place.
To the issue of playing it on two days vs one day vs two different weekends:
Personally I would want it to happen over two consequtive day because I want the top 4 double elimination to be happening 1 match at the time. This will take up to 2 hours, with 7 matches if the winners bracket gets reset. A 8 player round robin will take about 2 hours to complete, with fast timer and best of 3. This makes the whole thing about 4 hours, which to me sounds a bit long for potential viewers and players. But then again, some of the larger fast timer tournaments have been pushing 4 hours too, so maybe I should just push forward for 1 day?
Having it be about 4 hours on one day makes scheduling harder, if there are large enough time zones, which is why having it on two days seems appealing.
Having on two different weekends seems like blowing up a balloon, and letting the air go out slowly. I would want to avoid that as much as possible.
In the end, I would have to work these dates out with the top 8 when the top 8 is decided, at which point I would hope it all magically fits together. But rest assure I will do my best to comply with the wishes of the finalists when they have been decided!