I am a US citizen and I want to visit friends and travel in China.

I live in Arizona but will be in L.A for one day. Is it attainable to get my visa in one business day or drop it off and have it sent to my home? How much would that cost?

Secondly, I already have an invitation letter from a Chinese citizen and round-trip flight proof but I am considering changing the date of my flight to one week earlier. Is it okay to submit a visa application with a different flight date? I am not sure when I will get my flight changed or if I am even able to.