Night Person (Fallout Supplement)
From D&D Wiki
As a night-time person, you are more awake and alert when the sun goes down. Your eyesight and Dexterity are improved at night.
Prerequisite: Level 6
Benefit: When the sun is down(Or 8PM to 6AM), a Night Person gains +1 to both Spot & Search checks and Dexterity. This perk directly affects your “internal clock” and remains active both inside and outside.