How many times is night invoked in Shakespeare's Macbeth?

There are two significant times when night, or darkness, is invoked in the play. Darkness and the night are symbols throughout the play, but the literal invoking of the night is accomplished by Lady Macbeth. 

In Act 1, scene 5, Lady Macbeth invokes the night to help with the killing of King Duncan. 

LADY MACBETH:Come, thick night, / And pall thee in the dunnest smoke of hell, / That my keen knife see not...

There are two significant times when night, or darkness, is invoked in the play. Darkness and the night are symbols throughout the play, but the literal invoking of the night is accomplished by Lady Macbeth. 

In Act 1, scene 5, Lady Macbeth invokes the night to help with the killing of King Duncan. 

LADY MACBETH: Come, thick night, / And pall thee in the dunnest smoke of hell, / That my keen knife see not the wound it makes, / Nor heaven peep through the blanket of the dark / To cry "Hold, hold!" (I.v.57-60)

She calls for the "smoke of hell" to cover the knife as Macbeth goes to kill Duncan. The literal darkness becomes a symbol for the dark acts that the Macbeths commit. 

This invocation is flipped when Lady Macbeth begins to feel guilt over the murder. In Act 5, scene 1, Lady Macbeth insists on a candle to protect herself against the evil forces she has summoned. 

DOCTOR. How came she by that light?

GENTLEWOMAN. Why, it stood by her. She has light by her continually. 'Tis her command. (V.i.23-25)

These two instances of night being invoked are in communication with each other, bookending Lady Macbeth's appearances in the play and demonstrating the arch of her actions and remorse.