GZ to HK and back to GZ

If you want to leave from Guangzhou East station, the earliest train to Shenzhen leaves at 06:15am with the durition of 01h19m, and the earliest one to Hongkong leaves at 08:19am with the durition of 01h58m. You can make the purchase on site on your travelling day as there are many trains available everyday. But you'd better avoid travelling during the public holidays, like christmas day and new year holiday.