When is the best to tour both the Forbidden City Beijing. Summer Palace and Tiananmen Square?

I want to start my day tour fairly early and see many areas. You mentioned that it will take roughly 3-4 hours to walk around the Forbidden City. Can I cut that short in order to see some of the other surrounding sites? Like Drum/Bell Tower, Prince Kung Mansion, Beihai Park, Ming Tombs and the Beijing Tower in day? Many sites close way too early.