When does a turn begin and end? Is the daytime part of the rota?

According to the Shafi'i school, the basis of the rota is the night, from sunset to dawn, with the day following the night; for a husband who works at night, the basis of his rota is the day.
Allah made the night for rest (al-Anʿam 6:96), and ʿAisha r.a. related that the Prophet ﷺ rotated fairly among his wives (Sahih al-Bukhari 5212 mentions the turn Sauda gave to her). During the day of one wife's turn, the husband may stop by another wife's home for a need without staying the night or being intimate. A common problem in Malaysia is coming home late on one wife's turn but early on another's; consistency in the time of returning is also part of fairness. If work schedules vary, agree the method of counting in writing. See the question on night shifts and The rota in practice.