1 week voting period is a reasonable middle-ground I don't think it need any change.
An idea I would like to propose is to add more categories to the current rating, such as "game-feel/juice", "understandability", or "design intent".
I would use the following definitions:
Game-feel/juice
Does the game provide tactile feedback as you interact with the game world? (having both visual and audio feedback for interactions will be better)
Understandability
Does the game communicate its gameplay rules in an understandable manner? (the simpler and easier it is to understand, the better)
Design Intent
This one is a bit tricky, since the developers will need to specify the intent of the game they're making. It can be.. does the gameplay match with the theme the game is trying to be? Or, does the game elicit the supposed feeling? Or even, does the game fit well within the genre it is trying to become?
I am proposing this so that it would encourage all of us to be better game designers. Hey, this game jam is supposed to help everyone make better games, right?
Submissions that are still in very early stage will clearly have low ratings with the above definitions, but it should not matter as long as we strive to become better designers.
This is just my idea, please take it with a grain of salt.