Hello, I did Spooktober 2025 so I think I can answer some questions! :)
First of all, the jam starts on the 1st of September as opposed to the 1st of October. This is explained in the FAQ as being because a lot of people play horror games in the lead up to Halloween and having the game be published by the start of October allows it more visibility.
Secondly, before the jam begins, you're allowed to make concept art alongside writing the outline to the story and the log line. Excluding the log line, nothing you do before it begins is allowed to be used directly within the game. This means you're not allowed to do scripting or asset creation.
I would definitely recommend giving the FAQ a read through on the overview page of the jam, I hope this helped!