Information needed to obtain a tourist visa to visit family in China

We are planning to visit our daughter, son-in-law, and grandchild in the last 2 weeks of October of 2012. We will fly from Chicago to Beijing to meet them, visit the Great Wall, travel to Xian to see the T. Warriors then fly on the their city (Xining) and staying with them for the rest of the 2 weeks visiting. They are American students in Xining. At the end of the 2 wks we will fly to Beijing and then back home to Chicago. Besides the Visa application, photo, application fee, and our valid passports what else is required to obtain the tourist visit. We have booked e-tickets for the flight to and from Beijing. Do we need some kind of invitation letter? If we apply on a weekday morning can we get the visa in the afternoon since we must travel from down state Illinois to apply?

Thank You, Charles M.