Originally Posted by jiejie

I would not do this trip this way at all. Due to high possibility of weather delays this time of year with flights (in addition to the usual ATC delays), I would stay with trains on some routes. I recommend you reorder the itinerary and do the following, making arrangements quickly so you can get the tickets that make this work. Order HK > Shanghai > Beijing > Xian > Guilin > HK.

6/28 morning flight HKG-PVG on Hong Kong Airlines 08:15-10:50. Forget about Shenzhen on this, the differential after you spend cash getting to SZX is negligible, and it wastes time that you don't have.
6/30 late afternoon train Shanghai to Beijing. The G22 in 1st class seat is available. 17:00-22:16. You need relatively less time in Shanghai and more in Beijing.
7/4 overnight train Beijing to Xi'an. The Z19 in soft sleeper is available and recommended. 20:41 from Beijing West arriving on 7/5 08:15 into Xi'an main.
7/6 late morning flight Xi'an-Guilin on China Southern 11:20-13:10. Get forthwhip to Yangshuo and spend your time there.
7/9 Two decent options: A: Fly KWL-SZX on CZ flight 08:10-09:10, then shuttle bus to Hong Kong. You'll still have some free afternoon time in HK. Looks like no nonstop KWL-HKG available that allow for a comfortable connection to an international out of HKG. Option B: first fast train D2831 Guilin North to Guangzhou South in 1st class seat 08:00-10:44 is still available. Shuttle bus or private car to HKIA. Unfortunately Guilin-Shenzhen fast train meeting your schedule reqmts is already sold out. Flight schedule slippage/delay is possible; train will almost certainly run on time.