I want to make a cheesecake but with only a half-recipe of filling because I want an 8-serving cake instead of a 16-serving cake. I'm using a recipe that calls for baking the cake in a water bath in a 9-inch springform pan. How should I adjust the cooking time? The recipe for the full cake suggests 90 minutes. My oven door doesn't have a window and I want to minimize the number of times I have to open the door to check on the cake.