The way I see it right now, the worst-case scenario would be that tomorrow, Friday, and Monday are the showcases for Powdered Toast Man, Zim, and Reptar (in whatever order they decide), and the day of launch will see the reveal of the Avatar characters, and then the day after would be their showcases.
In other subjects, how long are people's respective "Potential Main" lists? Because as of now, just looking at the characters that have been showcased, I've got seven:
SpongeBob
Lincoln
April
CatDog
Helga
Danny
Oblina