You have to make them public before the final submission date so that the judges, the other jam members and the general public can play them.
What a few of us did in the first jam was to make it private with a password and invite testers to test it and provide comments via this forum. It's probably okay to provide the password in the forum, as only people interested in the jam are likely to read it. Do this as early as you can, so that people have sufficient time to test your game, provide comments to you and you can address the comments before the final submission date. Remember that the most likely testers are probably working on their own games as well, so they may have limited time.