Hi Daniel, Jams are great for motivation and interacting with others.
Generally the rules of any jam give clarity - for this one your product page must have gone up between the start of the Jam to the end date. So if you're trying to submit a project you published in January - it would be breaking the rules. Beyond that, between now and the end is good to publish and submit (that's true for many jams).
Once it's done and the game page on itchio is complete/published, all that jazz, you'll come back to the Jam's homepage where you'll see a "Submit Your Project" button. A pop-up with a dropdown menu will appear and your game/project should be listed there for inclusion.
And don't forget to come back later to rate and comment on the other projects in the Jam. Interacting is a good practice with any jam.
Hope that helps!