Agreed on the final knockouts. There should be at least 24hrs between each round. Most of us have to work after staying up all night playing catch up. Humans need to sleep at some point. 8 days in a row is too much for a fair competition. You'd have to take a weeks vacation to keep up with the people who play 20+ hrs…
You can do other levels but looks like you get more stars for new ones. I had a streak of super and nightmareishly hard levels during the final rounds but still fun.