In the name of Allah, the Most Merciful, the Bestower of Mercy.
A number of brothers have asked regarding which day and time they should enter into I’tikaaf this year.
As a general principle, the period for I’tikaaf begins when a person intends for it to begin. It is permitted to observe I’tikaaf for more or less than ten days. However the practice of the Muslims throughout centuries has been to observe I’tikaaf for the last ten days of Ramadhan.
The Prophet (sal Allaahu alayhi wa sallam) himself used to regularly observe I’tikaaf for ten days in Ramadhan, however Abu Hurairah (may Allaah be pleased with him) narrates,
During the final year in which the soul of the Prophet (sal Allaahu alayhi wa sallam) was taken, he observed I’tikaaf for twenty days. 
In relation to a person who makes an intention to observe I’tikaaf for ten days, then he should enter into the Masjid with the correct intention on the night of the 21st fast just before Maghrib time. It is important to note that Islamically, the night precedes the day. Therefore, before Maghrib it is the day of the 20th fast, however after Maghrib of the same day we enter into the night of the 21st fast.
This year, 2023, the day of the 20th fast will be Tuesday 11th April.
As soon as Maghrib enters, this then becomes the night of the 21st fast.
Therefore it is upon those observing I’tikaaf for ten days to enter into the Masjid on Tuesday 11th April, before Maghrib.
We ask Allah to accept the fasting and praying of the Muslims during Ramadhan, and to forgive our sins.
Abul Abbaas Naveed Ayaaz
20th Ramadhan, 1444h
Corresponding to 11th April, 2023
 Narrated by Abu Hurayrah; Collected by Bukhaaree