How does the nocturnal setting of Act II, scene i contribute to the scene's over all mood, or atmosphere?

It is a classic horror device to use the darkness of night
to create suspense.  Interestingly, in the Globe Theater of Shakespeare's day, the play
would have been performed in full daylight (approx. 3pm) and so, there would have been
no opportunity for the audience to experience this mood-setting nighttime scene except
through the actors use of text and props (like torches to indicate that it is dark) and
their own imaginations.

That said, Shakespeare makes sure
to exploit some devices that we commonly associate with "things that go bump in the
night" to assist in the overall foreboding and suspenseful atmopshere of this "nocturnal
setting:"

• Banquo and Fleance discuss that the
  hour is past midnight, a sure indication that danger/evil is
  afoot.


• Banquo speaks to Fleance of a premonition ("A
  heavy summons lies like lead upon me") and also of his bad dreams ("cursed thoughts that
  nature/Gives way to in repose.")


• Upon Macbeth's entrance,
  a jumpy Banquo asks for his sword and calls out, "Who's
  there?"


• Macbeth, once he is alone onstage in darkness,
  can't decide if a dagger really floats before him, or if his imagination has put it
  there.


• Macbeth uses 7 lines of his soliloquy to create a
  suspenseful sense of the time and place:

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. . . Now o'er the one
half-world

Nature seems dead, and wicked dreams
abuse

The curtain'd sleep.  Witchcraft
celebrates

Pale Hecate's offerings, and wither'd
murder,

Alarum'd by his sentinel, the
wolf,

Whose howl's his watch, thus with his stealthy
pace,

. . .Moves like a
ghost.

• A bell
  breaks the silence to toll the hour that Macbeth must go and commit the murder, a creepy
  sound in the dead of night.

There are
indications of dramatic enhancements to this scene  -- the men whispering by torchlight,
the surprise entrance of Macbeth, the potential sound effects of the bell and wolf's
howl -- and yet it is the text itself that Shakespeare mainly relies upon to create the
suspense and foreboding of this late night scene, a suspense that relies heavily upon
the audience's imaginations.

For more on Act II, scene i
and Macbeth's famous dagger soliloquy, please follow the links
below.