The 1 hour playtime rule is mostly there just so that we have a hard cap on how long a judge has to spend on any one game. The overall length of the game won't be a factor in the judging other than 1. Judges aren't required to play longer than one hour, and 2. You have communicated what you want to with your game. If it is 30 minutes and you communicated the game to us, you're fine.