How much time will players spend with your game in one sitting? The answer affects many aspects of your game's design, and you can remove the guesswork from it by thinking about the environment that surrounds your game and how that affects players' engagement with it. Are they at home, unwinding in front of their console? Or are they out for lunch, sneaking in turns between bites of food? Test the game in these environments, and learn how they affect the amount of time players are willing or able to put into your game. Then you can choose to design towards those constraints or perhaps decide that you need to move your game to a new environment (e.g. new platform, genre, or monetization method): in either case, recognizing those needs early will help you develop a better game.