It would take 10 to 20 days to recite the Prabandha Parayana in Sri Rangam. Sri Tirumangai Azhvar arranged to recite Swami Nammazhwar’s prabhandhams in front of Namperumal. This began on Vaikunta Ekadasi and continued for nine days . Today this period is referred to Iraappattu or Tiruvaymozhi Tirunaal. It is a 10-day event, after which the Azhwars used to return to their respective Divya Desas. The whole sanchara took about 2 months. Due to this event, the Prabandhas were not read in those temples. This time period is termed as Anadhyayanakaala. Incidentally, Kuraththazhwar's Tirunakshathram coincides with the return of Azhwar's tirumeni.
Therefore, the Prabandhas were in houses and temples starting on Kuraththazhwar Tirunakshathram. This followed through as a custom in all Divya Desams. Moreover, as a tradition started by Tirumangai Azhwar, Divya Prabandhas will not be read from Tirumangai Azhwar Tirunakshathram onwards.
A few hundred years later, Bhagavan Ramanuja energized this tradition and made changes. This is been recorded in Tiruvullam of Nathamuni. Sri Ramanujar added ten days before the Ira Paththu and called them Pagal Paththu. During Pagal Paththu, he established that all Azhvar prabhandhams be recited.
Also, Sri Ramanuja added an additional day before Pagal Paththu to recognize Tirumangai Azhwar’s contribution. It would begin with reciting TiruNedunthandagam of Sri Tirumangai Azhwar in front of Namperumal at Srirangam. The original 10-day festival was therefore extended to 21 days by Sri Ramanuja.
The LORD commands, “I and my two Nacchiyars will be seated in the simhasana during the pagal patthu and irappathu utsavam days and will listen to all Azhvar Arulicheyals. Elsewhere, until then, no one should recite them”.