Hi, just to clarify you should only start when the jams starts.
It's encouraged that the submissions are made within the period of the jam as there is also a theme for you to build upon your soundtrack. All submissions of the jam must be original and composed specifically for the jam, hence the rule of being unreleased, and the rule of being unfinished is that it would be unfair to other participants (as this a ranked jam) if you have more time than the others. Your submission would be considered illegitimate if it is found that you have submitted something that is made before the jam starts.