I have a flight on a Sunday Morning at 8:20 to Shanghai from Shenzhen.

It is with Hainan Airlines. I understand that I should be at the Airport at 6:20. I am staying in HK. Should I cross the day before from HK and stay overnight in SZ? Or should I cross early in the morning from HK? If I were to stay in SZ Downtown how would I get to SZ Airport in the early morning?

Thank you.