This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You may want to have a look at Joda Time, I believe some variation will be included with Java 1.7, and it makes for easy time/date calculations. I don't believe it will remove the weekends for you, but could make it a bit easier.