Waiting time has no bright-line rule — the regulations say plainly that whether it counts as hours worked “depends upon particular circumstances,” requiring a look at the agreement between the parties, how they actually apply it, the nature of the job, and its relationship to the waiting itself. The Supreme Court framed the whole inquiry in one contrast: the facts may show that the employee “was engaged to wait,” or they may show that he “waited to be engaged.” The first is paid work; the second is not. Deciding which one applies to a given stretch of idle time is, as the courts put it, a matter of “common sense and the general concept of work or employment,” not a formula.

On-duty waiting looks like this: the employee cannot use the time effectively for personal purposes because it is unpredictable, usually short, and still controlled by the employer. A stenographer reading a book between dictation, a messenger doing a crossword between assignments, a fireman playing checkers between alarms, and a factory worker chatting while machinery gets repaired are all, by the Department’s own account, working during that inactivity — the waiting is an integral part of the job, so they were engaged to wait for it. That holds even away from the employer’s premises: a repair worker waiting for a customer to get the site ready is still on the clock, and a worker can be working during downtime even if free to leave the building, because what makes the time compensable is that it belongs to and is controlled by the employer, not where the body happens to be standing.

Off-duty time flips every one of those conditions. To not count as hours worked, the employee has to be completely relieved from duty for a stretch long enough to use effectively for their own purposes — and critically, they have to be definitely told in advance that they may leave and will not have to report back until a specific, named hour. Whether a given block is long enough is a question of fact, not a set minimum, but the advance, definite release from duty is the non-negotiable piece — without it, the employee is still waiting to be engaged, not free. A related but distinct question is on-call time: an employee required to remain on the employer’s premises, or so close to it that the time cannot be used effectively for personal purposes, is working while on call, while an employee who is merely required to leave word at home or with company officials where they can be reached — without being tied to the premises — is not.