hours scheduled divided by number of months
Is your report really that simple? What if the start date is on the last day of the month? Are you going to allocate the same number of hours for that month as all the others? What about allowing for weekends and (shudder) holidays?
I hate to answer a question with more questions so I will close by offering a few hints. You'd probably have a more accurate report if you step through each date in your range and decide if that's a valid work day. You can do this with
Java's Date class, or even better with the Calendar class. Either of those will allow you to check the month, so you can add each work day to a monthly total.