So God created man in his own image, in the image of God he created him; male and female he created them.
#genesis 1:27 #beireshit

Adam wasn't both male and female or else he would have been complete by himself. He was only male so that he'd know he needed a wife. "It is not good that man should be alone."

Male and female were created on the 6th day in the same sense that all mankind was created on the 6th day: by proxy in the person of Adam. Eve was present in Adam in the same way that we were. We were all created on the 6th day.