Is it permissible to perform Salat al-Istikhara immediately after every prayer or before it? And what are the conditions for its validity and acceptance?

Istikhara is a supplication transmitted from the Prophet, peace and blessings be upon him, and it is prescribed when one is hesitant about a permissible matter. It is sunnah to repeat it. Istikhara is not prescribed without a need, especially not after an obligatory prayer, because it is to be performed after a supererogatory prayer. The conditions for Istikhara are the same as the conditions for supplication, because it is a supplication.