Boyd’s Bible Dictionary:

The Hebrew day, from sunset to sunset, embraced the entire night
(Gen. 1:5). Death (John 9:4); sin (1 Thess. 5.5); sorrow, sin, and death (Rev. 21:25; 22:5).

Concise Bible Dictionary:

Used symbolically for:
1. Death, a time “when no man can work” (John 9:4).
2. The moral darkness of the world, in which men sleep and are drunken (1 Thess. 5:7).
3. The period of Christ’s rejection, which is far spent, and the “day” at hand (Rom. 13:12). There will be no night of moral or spiritual darkness in the heavenly Jerusalem (Rev. 21:25; Rev. 22:5).