GTA cities at night are different places. Trailer 2 is committed enough to night content that we can read it as a real piece of the game's atmosphere rather than as a stylised sequence.
For the daytime equivalent, see the aerial shots breakdown.
What the night frames show
The art deco strip lit. Neon signs, club exteriors, headlight glare on wet pavement. Mid-shot of a club entrance with patrons queuing. A driving sequence at night through downtown. A wetlands frame with lower visibility.
Detail is preserved - which is harder than it sounds. Many open worlds drop detail at night to mask rendering load. Trailer 2's night content does not.
Why night matters
Some content lives at night - clubs, strip clubs, late-night business. Some content reads better at night - the art deco strip is at its strongest after dark. Some content shifts behaviour at night - police presence, NPC density.
GTA V handled night well; GTA 6 looks like it handles night better.