The most common and most likely answer to this crossword clue is the 6 letter word NIGHTS
I've seen this crossword clue in Financial Times
N
I
G
H
T
S
More clues leading to the result NIGHTS
- Men on board reported dark times
- Spooky things when most people are asleep?
- When things go bump?
- Near to shelter, originally in darkness
- When everything goes dark at one point: sight aberration
- Things lost in darkness
- Dark times, strange things
- Heard men of the Round Table evenings
- “Dark Times on the Horizon,” by Eliot
Buddy explains!

The straight part
We know that "most people are asleep" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case most people are asleep = nights.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does NIGHTS mean?
NIGHTS adverb- At night.
- Every night.
- The period between sunset and sunrise, when a location faces far away from the sun, thus when the sky is dark.
- (Astronomy) The period of darkness beginning at the end of evening astronomical twilight when the sun is 18 degrees below the horizon, and ending at the beginning of morning astronomical twilight.
- (Legal) Often defined in the legal system as beginning 30 minutes after sunset, and ending 30 minutes before sunrise.
- An evening or night spent at a particular activity.
- A night (and part of the days before and after it) spent in a place away from home, e.g. a hotel.
- Nightfall.
- Darkness (due to it being nighttime).
- A dark blue colour, midnight blue.
- A night's worth of competitions, generally one game.