Your game may be as short or as long as you like, that is up to your vision for the game an what you think is best.
You can also take a look at the judging criteria to get a sense of how they will be scored. Do keep in mind that if there are 100+ entries - then if games require hours to complete the judges may have time not play such games to full completion. The judges will of course make a best effort to play, experience and get a good sense of each game.
