If you run out of time near the end you can aim "something playable". If the players like a too short game, they will sometime ask for a more levels after the Jam and they have an option to follow you on itch.
The first time you publish the game on itch.io it can be long. Try to publish one hour before the end of the Jam, at least.It can be very fast to publish your game but it's risky to wait to much. If you don't change the game file, you have time to polish the game description after the deadline, or add pictures on itch.io.
Don't forget to take a beautiful picture of your game when you try it, for your cover on itch.io. :) (optional and can be done after the deadline)