A calendar
Four days a month set by the moon, when the rules tighten for everyone at once — and then release.
Lay people may take the eight precepts — for this day and night only.
Nothing eaten after noon. Plainer surroundings, less entertainment.
A visit to the monastery, and teaching or listening to it.
Longer sitting than usual. Then the ordinary rules return.
The day is fixed by something nobody controls, not chosen for convenience, and everyone is on it together. The precepts are taken, and taken again, each observance: a part-time renunciate identity for one day, renewed rather than kept.
Monasteries welcome lay visitors on observance days. Lay and monastic observance differ; you'd be keeping the lay one.