Spiritual Retreat: Performing an Obligatory Qadaʾ Iʿtikaf
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1764
Performing an obligatory qaḍāʾ iʿtikāf is not an immediate obligation (al‑wājib al‑fawrī).[1] However, making it up must not be delayed to such an extent that it would be regarded as being careless in accomplishing the obligation. And the recommended precaution is that it should be made up immediately.
-Ayatullah Sistani, Practical Laws of Islam, Spiritual Retreat (Iʿtikāf)
1
This is an obligation that must be performed as soon as it is possible to do so, and delaying its performance is not permitted.