When does one enter and exit the mosque for Iʿtikāf during the last ten days of Ramadan?

Firstly: According to the majority of scholars, I'tikaf (spiritual retreat) begins before sunset on the night of the twenty-first. They base this on the fact that the Prophet, peace be upon him, used to perform I'tikaf during the last ten nights of Ramadan (definition), and Laylat al-Qadr (the Night of Decree) is sought during these nights. They interpret the hadith (definition) of Aisha, may Allah be pleased with her, which indicates his entry after Fajr prayer, as meaning that he secluded himself in his place of I'tikaf after Fajr prayer, not that it was the time I'tikaf began. Some of the Salaf, however, held that one enters I'tikaf after Fajr prayer.

Secondly: The one performing I'tikaf exits when Ramadan concludes, at sunset on its last day. It is recommended for him to remain in his place of I'tikaf until he prays Fajr and then leaves for the Eid prayer.