The first three weeks of the schedule is set. Remember, CBS will no longer have the exclusive 3:30pm window for their SEC on CBS national game. That being said, the SEC on CBS will retain the first pick, working with the conference, for the 3:30 time slot.
The way it worked last year was the SEC Network had up to 3 game slots per Saturday, typically around the noon, 4pm, and 8pm hours. Usually, the SEC worked to only have one other game against the CBS game. Also, ESPN grabs games as they see fit, such as the South Carolina at Georgia game on September 19th.