Travel from Hong Kong airport to Guangzhou by train

I arrive at Hong Kong airport at 1pm from Australia on Saturday1 Feb 2025 (forth day of Chinese new year, may be busy time) I like to arrive at Guangzhou taking Hong Kong airport express train to West Kowloon and then high speed train to Guangzhou. Due to the festive season, can I still buy ticket from airport train counter or should I pre-purchase? If pre-purchase, what is the website to buy the ticket and how long after flight landing should the train depart from airport to allow enough time?