Chance of tickets being sold out, Guangdong

So, this website advises to buy them in advance, since they can sell out.
I'm planning to stay in Guangzhou from July 1 to July 14 and during this time plan to visit several locations outside Guangzhou, but still in Guangdong.
However for me it would be practical to buy them to certain locations on the day of the travel, since right now I cannot predict if I will be willing to go to some of these locations on a certain day/time (mood, weather, etc.) - I don't want to buy them right now in April.

So I would like to ask you for experience, how probable it is that these rail connections will be sold out in the first half of July this year:
Guangzhou - Foshan (want to visit the CCTV Nanhai Movie and TV Town)
Guangzhou - Shenzhen (want to visit the Window of the World)
Guangzhou - Huizhou (want to visit the Luofu Mountain National Scenic Area)
Guangzhou - Zhongshan (want to visit Sun Yat-sen's Former Residence)
Guangzhou - Zhaoqing (want to visit the Seven Star Crags)
Guangzhou - Shaoguan (want to visit the Danxia Mountain)

Every single one of these destinations I want to visit for one day - thus take a ride from Guangzhou in the morning, visit the place, and then the same day take a ride back to Guangzhou in the evening, where I have a hotel booked.
What do you think - getting tickets for these connections on the day of the travel would be possible or not?
Thanks.