It depends on how the workday is defined. In California, overtime applies to hours worked over 8 in a workday or 40 in a workweek, and double time applies over 12 hours in a workday.
A workday is any fixed 24-hour period (commonly 12:01 a.m. to midnight). Overtime is calculated based on hours worked within that defined workday — not consecutive hours across two workdays.
For example, if an employee works from 4 p.m. to midnight (Day 1) and then 12:01 a.m. to 8 a.m. (Day 2), they worked 16 consecutive hours but did not exceed 8 hours in either workday — so no daily overtime is owed.
However, weekly overtime still applies if total hours exceed 40 in the workweek.
Employers should still consider safety and fatigue when scheduling long consecutive shifts.
Read about Overtime in the HR Library.