Brahmacariya: The celibate life
Brahmacariya names sexual abstinence undertaken for the sake of practice. A married couple clearing a season is borrowing the monk's discipline for a while, and the borrowing only works if the cleared time gets filled. Abstaining and then staring at the ceiling is an empty room with nothing moved in; the fasting and the praying are what make the emptied space worth anything.
Uposatha: The observance day
Uposatha is the set day when householders take on extra precepts, celibacy among them, and afterward resume ordinary life. Agreeing on a season and then coming together again has exactly this shape: the abstaining is fenced at both ends, entered by consent and left by consent. No open-ended vow is being asked of a couple here, and an undertaking with a known length is one a person can keep.
Attakilamathānuyoga: Devotion to self-torment
Attakilamathānuyoga is austerity pursued for its own sake, which the Buddha set aside as a dead end. Stretching the agreed season into an indefinite one is a lute string tuned tighter and tighter: past a point it stops making better music and snaps. Coming together again is the peg turned back, and turning it back belongs to the practice.
Kāmacchanda: Sensual desire
Kāmacchanda is the pull toward pleasant sights, tastes and touches, first of the hindrances. Pressed down by force, it behaves like a ball pushed under water: steady pressure, then a sudden rush to the surface. The lack of self-control that surfaces at the end of a long deprivation was there through the whole season, waiting, and pretending otherwise is how a couple gets caught.
Māra: The tempter
Māra works through desires a mind already holds. He brings nothing new to two people straining under a long fast; he finds the loose board and steps on it, which is why the danger is named as their own want of restraint. His daughters came to the Buddha at the height of his effort, and a devout season is just when a household should expect the visit.
Indriyasaṃvara: Guarding the sense doors
Indriyasaṃvara is restraint at eye, ear and the rest, the doorkeeper's work of deciding what gets let in and dwelt on. Control of this kind is built in ordinary weeks, so that a season set apart for prayer rests on something already standing. A couple who has never watched the door will find the fast unbearable and blame the fast, when the door was open the whole time.