Time & date guides

Short explanations for common time-calculation questions.

Decimal hours: the dot matters ↗

Decimal hours use fractions of an hour. Clock notation uses minutes out of sixty.

An earlier end time needs a date boundary, not a guess.

A date is a place on a calendar. An instant is a place on the timeline.

Your schedule determines what counts. Endpoint choices determine where counting starts and stops.

Two places may change their clocks on different dates—or not change them at all.

The same digits can describe different instants when their units change.