Shenzhen airport to Hongkong airport by subway

I guess you may think about the ferry and bus instead of subway. Some online information says there are buses available between shenzhen and HK airport and would take about 2 hours. The bus available about every 30min to 1 hour. As for ferry, there seems available for 10:15; 13:15 and 17:00. The ferry would need about 40min to 1 hour. but you still need to leave at least 30min for the security check etc before ferry trip. You can contact the shenzhen and HK airport directly to double confirm the schedule to see if this is the newest one and then choose it based on your time.