When do I want to begin with a QA Inspector?
As soon as you complete the process of design or concept.
QAS is not part of the process of designing the project but the implementation of it. That said, many times during the course of the project engineers or field staff will find defects in the design, which the will need to addressed as soon as possible.
From our experience we have found deficiencies in many different designs elements, which must be resolved before commencement of work so initial design analysis is expected to be complete before work commences.
That said, the inspection process itself also finds discrepancies in assembly which must be rectified / rejected / reworked / repaired before allowing payment.