Day is the time of activity and wakefulness. Night is the Dreamtime that Day gives fuel to. Day recedes into Night, which gives birth to Day. In the darkness of Night, unconscious notions transforms to conscious choices in the light of Day. Day/Night complements each other.
In Western Cultures, masculine qualities would be more rational, direct, and assertive. Feminine qualities are creativity, vision, and introspection. Male is looking out; female looking in. With Day/Night, you move from duality to wholeness.