The earliest flight will be at 9:30am in the morning. It means you have to wait a few hours whatever you take train or airplane. The air ticket is cheapest in June, 40percent off for economy is available now. You can book earlier. All flights are China Southern Airlines. (The first train is K528 leaveing Guangzhou at 8:08am). See more flights here:
https://www.travelchinaguide.com/china-flights/