How long should our game be? Do you want a short game where you can get through all the content in a few minutes or would you prefer something on the longer side that would take a few hours to get through?
This is something that depends on preferences of each player. However, officially, there is no specification for the length of the game. Based on previous jam submissions, most games are short and simple (5 - 10 minutes), although there are some games which are long.