Venture Bros. makes an appearance on Sunday night at midnight, which is the first time it's been on Sunday night in a good while. While I don't think that's the season four premiere, it's possible that is the start of a couple weeks of episodes that will lead into season four's start. Right before season three started they showed the last two episodes leading up to it, and given the cliffhanger-ish nature of the show, it makes a lot of sense.
As I said, I'm still totally guessing here, but the start date for season four is potentially around mid-October (which goes with what Jackson mentioned as a start date). Stay tuned!