Possible Clues:

• Light snow worried those staying up late
• Early birds' opposites
• Stay-up-late types
• Ones late to work?
• Late sleepers
• Late partygoers provide their own lights
• Lights now required for those who get busy after dark
• *Baying?
• Hard-to-see critters lurking in 20-, 28-, 33- and 43-Across
• Are they wise when others have succumbed to darkness?