The cycle

The countdown runs for one interval (20 minutes by default). Then:

Heads-up. A small pill appears: “Break in 1:00”. It has Start now and Snooze 5m buttons. The default heads-up is 60 seconds.
Wait for a pause in typing. When the heads-up ends, the break starts only if you have not used the keyboard or pointer for 2 seconds. If you are still typing, the pill reads “As soon as you pause…” and the break waits. It waits at most 30 seconds past the end of the heads-up. After that the break starts anyway.
The break. A full-screen overlay covers every display for the break length (20 seconds by default).
Cooldown. After the break ends or is skipped, a 30-second cooldown runs. Nothing becomes due during it. The next break is due one interval after the break ended.

Long breaks

Long break every is set to “never” by default. If you set it to n, every _n_th break uses the long break length (5 minutes by default) and the long break messages.

Office hours

Limit to office hours is off by default. When it is on, a break that comes due outside the active days and hours is postponed. The countdown restarts for a full interval, and the postponement does not count against your score.

Time away from the Mac

Idle. If you give no input for the time set in Away counts as a break after (1 minute by default), GazeKeeper counts it as a break and restarts the countdown. It records one such break per rest.
Sleep, screen sleep and screen lock. The schedule stops while the Mac is away. If you were away for at least the break length, that counts as a break and the countdown restarts. If you were away for less, you get 60 seconds in which no break can become due.

Calendar awareness

Settings → Calendar → Offer breaks before meetings is off by default. Turning it on asks for calendar access. GazeKeeper reads meeting start times for the next four hours. It treats an event as a meeting if it is not an all-day event and has more than one attendee, a location, or a URL.

The rule is narrow: a break that would be due in the last two minutes before a meeting is moved to three minutes before the meeting starts. A break due earlier, or during a meeting, is not changed. During a call the detectors hold the break.

If you add or move a meeting, GazeKeeper reapplies the rule to the pending break. If you cancel one, the earlier time stays. If calendar access is off, the setting has no effect and Settings says so.

Postpone and skip

Snooze moves the break out by 5, 10 or 15 minutes from the menu, or by 5 minutes from the pill, the break screen, a shortcut or Shortcuts. Each due break allows 2 snoozes by default. The count resets when the break starts. When none are left, the snooze controls are disabled.
Skip ends a break that is on screen. The Skip button appears after the first 3 seconds of a break. Esc also skips, if Allow Esc to skip is on.
Skip Next Break in the menu cancels the upcoming break and restarts the countdown. During the heads-up it counts as an ordinary skip.

Detector holds do not use up snoozes.

Pause

The menu pauses for 30 minutes, 1 hour, until tomorrow, or indefinitely. A paused countdown stops and continues from the same point when the pause ends. If you pause during a break, the break ends and is logged as interrupted.

Three things can pause the schedule: you, a detector, and a Focus filter. They are separate. The countdown continues only when none of them is active.