Don't wanna wait for the 12:15 ferry to Zhuhai after arriving HKIA at 6:45.

Instead of waiting so long, you can go through the immigration and check out. Then take Airport Express to HK Station. Walk to Central Station and take Island Line to Shueng Wan. Leave exit D and walk for around 350yd to HK-Macau Ferry Terminal, where ferries are also available. Try to catch the 09:30 schedule. It costs 175HKD per person and takes around 70min.