X2 visa extension

Hello,
I have a x2 type that will expire on Sunday 31st this month. I was given a recomdation letter from my uni to get a 30 days extension to travel and was adviced to get on the 30th of this month, not to loose days from the extension. However, im wondering if the office opens on Saturday? I live in Shanghai. Also, can i get two months or 45 days extension instead of 30 days?