A user wants to run a batch job repetitively, but requires that each invocation starts five hours after the previous run finishes. What strategy will accomplish this?

A background launch with sleep would start the timer immediately when the job is launched, not after it finishes, so the five-hour gap would not reliably follow job completion.

Using 'at' with a fixed average-time interval is unreliable because actual run times vary, meaning the next job could start before or too long after the previous one completes.

Cron schedules jobs at fixed calendar intervals regardless of whether a previous instance has finished, so it cannot enforce a delay that begins only after a job completes.

By placing an 'at' command as the last line of the job script, the job schedules its next execution only after it has fully completed. This guarantees a five-hour delay from job completion rather than from job start, satisfying the requirement that each invocation starts five hours after the previous run finishes.