You could be fasting for 11 hours or 20 hours, depending on where you live.
Ramadan is about encouraging pious behavior and devoting oneself to concentrated worship. That means excesses, like having sex and smoking, are discouraged. In fact, Muslims believe both the repercussions of sins and the value of good acts are multiplied during the holy days. And if you want to do a little good, check out 33 Little Acts of Kindness You Can Do That Are Totally Free.