More protective at night?

At our house it's more of a chain reaction.  Nikon is very in tune with my body language and whether I appear to be watching someone with suspicion.  If I take no notice, Nikon doesn't either.  Pan, being immature (just saying that as a fact, not in a negative way) tends to read Nikon.  If I see/hear something and am watchful or tell Nikon to "watch it", Nikon might give a "wufff" and then Pan will come over and try to figure out what Nikon is watching.  I can't say they are any more or less alert at night.

 Lily is much more alert at night. My theory is that there is so much noise during the day that a lot of little noises get washed out. At night, that doesn't happen. It's quiet for the most part, so the little noises are then noticed. She alert barks on a lot of stuff at night. Having her wear the thundershirt at night has really helped with that. She's much more relaxed now.

Jewlieee, that's a very good point. He may be picking up on sounds more accutely as there's less background noise. He's fine inside the house (He's never been in an apartment before, but he quickly learned the word "neighbors!", which for him means, no threat. Those people outside are fine and that door opening isn't one of ours)