is there a bus that will leave ocean park at 4am to go to the airport?

No direct bus available and you need bus transfer.
At early morning, you can walk northward to take bus no. N171 at ABERDEEN TUNNEL bus stop to DIOCESAN GIRLS' SCHOOL, walk eastward for 100m then turn to the south for 150m to transfer to bus no. N11 at Kowloon Union Church, Jordan Road to Terminal 1.