During the rains it was difficult to move without injuring insect life. But the object was for study and meditation. In Tokhara the retreat is said to have been in winter, from the middle of the 12th to the middle of the 3rd moon; in India from the middle of the 5th to the 8th, or the 6th to the 9th moon; usually from Śrāvaṇa, Chinese 5th moon, to Aśvayuja, Chinese 8th moon; but the 16th of the 4th to the 15th of the 7th moon has been the common period in China and Japan. The two annual periods are sometimes called 坐夏 and 坐臘 sitting or resting for the summer and for the end of the year. The period is divided into three sections, former, middle, and latter, each of a month.

The term 結制 refers either to (1) the act of 'binding'  結 a stricter 'system' or set of 'rules'  制 of monastic training in a formal rite that marks the opening of a retreat, also called 'binding the retreat'  結夏, or to (2) the entire period of time that the stricter rules are in force, which is also called the 'period of retreat'  制中 or 'during the retreat'  安居中. The end of a retreat 解制 is marked by a rite in which the 'rules'  制 are 'relaxed' or 'loosened'  解. The time between retreats 解間, literally the 'period'  間 of 'loosening'  解, is when monks in training may come and register in a monastery or terminate their registration and depart. All appointments to official positions in a monastic bureaucracy are formally confirmed at the start of the retreat and remain fixed for the duration of the retreat.

At Japanese Zen monasteries today there are two annual retreats, which go by various names: (1) the rains retreat 雨安居, summer retreat 夏安居, or summer assembly 夏會, and (2) the snow retreat 雪安居, winter retreat 冬安居, or winter assembly 冬會. The traditional length of time for a retreat in East Asia is ninety days 九旬, which is three months according to the Chinese lunar calendar. The dates recommended in Standard Observances of the Sōtō School are May 15 to August 15 for the summer retreat and November 15 to February 15 for the winter retreat. These dates accord with the schedule for 'middle retreats'  中安居 as established in the Sōtō School Constitution 曹洞宗制. The Constitution also allows for 'early retreats'  前安居 that begin and end one month earlier than middle retreats, and 'late retreats'  後安居 that begin and end one month later.

The retreat as it is observed in Buddhist monasteries around the world today is a ritual replication of the rains retreat (Skt. varṣavāsa) originally observed by monks in ancient India during the three months of the monsoon. The expression 'cloistered retreat'  禁足安居, still used in Japanese Zen, reflects the fact that monks were 'forbidden'  禁 to wander 'on foot'  足 during the rainy season. The Mahāvagga (III, 2, 2) suggests that, at some early stage in the evolution of the Buddhist monastic order, there was a system of two dates for the assignment of seats at temporary dwelling sites set up for the rains retreat: one at the start of the rains, and a second one approximately a month later that was intended to accommodate latecomers. Subsequently, a third assignment of seats was implemented at the end of retreats, ostensibly for the purpose of reserving places for the next yearʼs retreat, but actually to accommodate monks who planned to remain at the site for the eight or nine months of the year between retreats; that was called the 'intervening' (Pāli, antarā) assignment of seats (Dutt, Buddhist Monks, 56-57; idem, Monachism, 101–107). Modern scholars theorize that the phenomenon of permanent Buddhist monastic institutions evolved from that practice. Although monasteries came to be occupied on a year-round basis, the rains retreat continued to be marked by a ritual 'binding' and 'releasing' of the community, and the seniority of individual monks came to be reckoned by the number of annual retreats that had passed since they received the precepts and joined the order.

Monastic retreats have traditionally been understood within the Buddhist world to begin and end on the days of a full moon and last for three months, but there is much variation in their timing. Chinese sources attest to that variation in ancient India and Central Asia and evince considerable difference of opinions on the issue. The Chinese pilgrim monk Xuanzang 玄奘 (600–664), for example, reported in his Record of Western Lands 西域記 that in some countries in Central Asia the retreat ran from the 16th day of the 12th month through the 15th day of the 3rd month, because that was time of year when the rains were heavy 〔T 2087.51.872a14〕 . Chinese translations of Indian Vinaya texts accurately rendered the three times for the assignment of seats for a retreat as 'earlier'  前, 'later'  後 and 'in between'  中, but the influential Chinese Vinaya exegete Daoxuan 道宣 (596–667) seems to have misconstrued the intended meaning of those terms. In his Commentary on the Four Part Vinaya 四分律行事鈔 Daoxuan wrote that the 'early retreat'  前安居 begins on 4/16 and lasts for three months; the 'late retreat'  後安居 begins on 5/16 and also lasts for three months; but the 'middle retreat'  中安居 begins any time from 4/17 through 5/15 and does not necessarily last for three months 〔T 1804.40.38b23〕 . The present day Sōtō interpretation of the three times for commencing retreats (early, middle, and late) derives from Daoxuanʼs interpretation of the Indian Vinaya tradition. The Brahmāʼs Net Sutra 梵網經, a Chinese apocryphon that is the locus classicus for the bodhisattva precepts 菩薩戒 used in East Asian Buddhism, says that disciples of the Buddha should enter into retreat for austere practice 頭陀 and sitting meditation 坐禪 twice a year, once in the winter and once in the summer 〔T 1484.24.1008a13〕 ). It is the oldest source to mention such a system, which may have begun in Central Asia or China. The practice of holding two annual retreats was well established in the public monasteries of Song dynasty (960-1278) China that served as a model for Japanese Zen (Skt. varṣa, vārṣika, varṣā, varṣās, varṣāvasāna varṣôṣita; varṣaṃvasitavyam, varṣâuṣitāḥ, varṣāvasitavyā, varṣôpagata, varṣôpanāyikā; Pāli vassa).