= Solution
Set the availability indicator $Y_i(t)$ to zero during the three-day recovery interval after each headache. Keep each episode's endpoint, but delay its entry to the previous headache time plus three. The calendar-time rows become
|| Patient
|| Next-event episode
|| Start
|| Stop
|| Event
|| $z$
| 001
| 1
| 0
| 24.8
| 1
| 0
| 001
| 2
| 27.8
| 33.1
| 1
| 0
| 001
| 3
| 36.1
| 40.2
| 1
| 0
| 001
| 4
| 43.2
| 51.9
| 1
| 0
| 001
| 5
| 54.9
| 60.0
| 0
| 0
The first interval still begins at zero because the patient was already headache-free for at least seven days before treatment. The recovery gaps supply no at-risk exposure and no partial-<likelihood> risk-set membership; they should not be retained as ordinary event-free at-risk time. If recovery extends past administrative closure, no subsequent eligible interval is created. This is a <refractory period in recurrent-event analysis>, represented by availability rather than by changing the event times.
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