Cut-off Ruler

Key point

a cut-off counted back from a departure

A cut-off two days before a departure reads three ways, and they only agree by accident. A DST change can make the three land an hour apart, or make two of them coincide.

Calendar days keep the departure’s time of day. Exact hours are elapsed time, whatever the clock does. A pinned local time keeps the wall clock you name and lets the elapsed time move.

1. The departure and the rule

A ship leaves New York at 18:00 on Monday 4 November 2024. The clocks went back on Sunday, so two calendar days is 49 hours, 48 hours lands at 19:00, and two days at 17:00 is 50 hours: three answers an hour apart.

DepartsAt local time

2. Three readings of "2 days before"

3. What cutoffAt returns

 

 

 

Worth trying: no clock change in between — calendar days and exact hours land on the same 18:00, and only the pinned reading differs. Then the spring-forward, where two readings coincide — 48 exact hours and the pinned 17:00 agree, by accident, and calendar days is the odd one out at 47 hours.

Reference: cutoffAt is the one call behind every reading here. See the guide’s two-days-before section, the scenario Two Days Before Is Not 48 Hours, and the DST Inspector for the general rule behind every gap and overlap a clock change makes.