Amount of minutes needed are generally from 48-75. If you want the greatest chance of good GS, 50-60 minutes would be considered the sweet spot. Do not game shape train if you are training someone. IF you have nothing but grandpas and you want to prepare for a tough game or playoffs, then by all means go for it. Game shape training doesn't guarantee that your players will pop. It is possible that it can work on injured players, since it is a team training skill.