Performance
Unions, parties, business owners, leaders and school boards each have a stake in when shops open and close, when schools and factories start, and how many hours people work and sleep. Because their interests clash, timing rules record who won, not a neutral optimum.
Who works, shops, studies or sleeps at which hours is the result of political struggle, not just habit. The division of day and night is fought over and settled like any other contested resource.
When, where and how people sleep, and what they think the night is for, differ widely between societies and keep changing over time. What feels like a natural rhythm of rest is largely a local custom.