Overnight shifts

Our night team works 22:00–06:00, Monday to Friday. How long is a shift, when does a job that needs 3 hours of shift time finish, how many hours does the team work in a week, and when does the next shift start after the weekend? This guide answers each with one call, in Rust, Python and JavaScript.

The scheduleCopy Anchor Link

One rule, in the Europe/London time zone:

• WorkDay: 22:00–06:00, Monday to Friday.

Because the end is before the start, each shift is overnight: it starts at 22:00 on its weekday and ends at 06:00 the next date. A shift belongs to the weekday it starts on, so Friday's shift runs into Saturday morning, and no shift ends on Monday morning, because none starts on Sunday (Rules: Overnight shifts).

The week of Monday 5 January 2026, in London time:

This page has no week strip: the strip draws working hours that end on the day they start, so it cannot show a shift that crosses midnight. The table above is the week it would show.

Count, extend and find shiftsCopy Anchor Link

Each tab counts Monday's shift, adds 3 hours of shift time to 04:00 on Tuesday, counts the whole week from Monday 00:00 to the next Monday 00:00, and finds the next shift after Friday's ends.

use jiff::civil::time;
use jiff::{SignedDuration, Zoned};
use workclock::{Schedule, Weekdays, WorkDay};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let days = Weekdays::MON_TO_FRI;
    let nights = Schedule::builder()
        .time_zone("Europe/London")
        .rule(WorkDay::new(time(22, 0, 0, 0), time(6, 0, 0, 0), days))
        .build()?;

    let monday: Zoned = "2026-01-05T22:00[Europe/London]".parse()?;
    let tuesday: Zoned = "2026-01-06T06:00[Europe/London]".parse()?;
    let shift = nights.between(&monday, &tuesday);
    assert_eq!(shift, SignedDuration::from_hours(8));

    let job: Zoned = "2026-01-06T04:00[Europe/London]".parse()?;
    let done = nights.add(&job, SignedDuration::from_hours(3))?;
    assert_eq!(done.to_string(), "2026-01-06T23:00:00Z");

    let week_start: Zoned = "2026-01-05T00:00[Europe/London]".parse()?;
    let week_end: Zoned = "2026-01-12T00:00[Europe/London]".parse()?;
    let week = nights.between(&week_start, &week_end);
    assert_eq!(week, SignedDuration::from_hours(40));

    let saturday: Zoned = "2026-01-10T06:00[Europe/London]".parse()?;
    let next = nights.next_period(&saturday)?;
    assert_eq!(next.start.to_string(), "2026-01-12T22:00:00Z");
    assert_eq!(next.end.to_string(), "2026-01-13T06:00:00Z");
    Ok(())
}

The resultCopy Anchor Link

• Monday's shift, 22:00 on Monday to 06:00 on Tuesday, counts 8 hours across midnight (DESIGN.md O1).
• A job started at 04:00 on Tuesday uses the last 2 hours of Monday's shift, waits through the day, and uses 1 hour of Tuesday's shift: it finishes at 23:00 on Tuesday 6 January. A shift already in progress counts from the query instant (DESIGN.md O4).
• The week from Monday 00:00 to the next Monday 00:00 has 40 hours, including the 6 hours of Friday's shift that fall on Saturday (DESIGN.md O5).
• After Friday's shift ends at 06:00 on Saturday 10 January, the next shift is Monday 12 January, 22:00 to Tuesday 13 January, 06:00. next_period returns the whole shift as one period, across midnight.

businesstimedelta 1.0.1 does not count across midnight: for the same rule it gives 0 hours for Monday's shift, and adding 4 hours at Monday 22:00 lands on Wednesday instead of 02:00 on Tuesday (Migrating from businesstimedelta).

Edge casesCopy Anchor Link

• A break inside the shift. A Break runs on the dates it starts on, like a WorkDay. A 02:00–02:30 break in Monday-to-Friday night shifts falls on Tuesday to Saturday, so give it those days: days=range(1, 6) in Python, ["tue", "wed", "thu", "fri", "sat"] in JavaScript. With the default Monday to Friday, Friday's shift keeps its break time and the week has 38 hours instead of 37 hours 30 minutes (Rules: Break).
• A holiday cuts a shift at midnight. A holiday removes calendar time, not whole shifts. With a holiday on Tuesday, Monday's shift keeps its 2 hours before midnight, and Tuesday's shift keeps its 6 hours after the next midnight (DESIGN.md HO1–HO3, Rules: Holidays).
• Daylight saving time (DST). A night shift that spans a clock change is an hour shorter or longer. London's clocks change at 01:00 UTC on a Sunday, so a Monday-to-Friday rota never spans one; with shifts every night, the night of Saturday 28 March 2026 has 7 hours and the night of Saturday 24 October 2026 has 9 hours (Time zones and DST: A night shift across a DST change).
• 24-hour shifts. A WorkDay whose start equals its end, such as 09:00–09:00, is a 24-hour shift (DESIGN.md O7–O9).

Not in 0.1.1: a different shift on one date, such as a short night on New Year's Eve. Shifts repeat by weekday, with no per-date overrides (DESIGN.md: Scope).

See alsoCopy Anchor Link

• Rules: the WorkDay rule and its overnight examples.
• Periods: next_period and previous_period.
• Payroll and overtime: contracted hours and overtime from a timesheet.
• DESIGN.md: WorkDay: the specification and examples O1–O9.