How Early Can I Get To Shekou Port for Ferry

I have a 10:20am flight from HKG but my stay is in Shenzhen. I used the ferry to get into Shenzhen but am now looking to book my ticket back. The only option available because of my flight is 7:15am. All the guidance online says I should arrive to the port for check in (+bag check) at 5:45am. But travel websites also say the port opens at 7:00am. Is this true? How early can I get to the port for a 7:15am ferry ride in order to have enough time to check in? Thank you