This should be scheduled some time after the system has been implemented, and I'd recommend it should be done no sooner than a month after. This isn't to say that the client and contractor will have no contact during that time, or that the system will operate flawlessly. Part of the reason for the Post-Implementation Review is to discuss the problems that have arisen since implementation as well as Lessons Learned.
Originator: Contractor and client.
Deliverable: Post-Implementation Review document. This is a summarization of the system's actual performance vs. expectations since implementation.
Phase 8. Implementation How it Works