The problem is that if you have a time that is 1:13 (one hour, 13 minutes). How does your client even know how to determine if the total is correct or not? They would have to know how to do the math correctly, which they would probably mess up even worse and you would have to explain how to convert time into a fraction so that they could verify the total. Unless you are rounding to 6, 15 or 30 minute increments, you should be using more than two decimal places for the fraction. If the client sees the number 1.3333 (1 hour, 20 minutes), they will know that that is not a time.