Engineering studies carried out preceding capital investment and initial operations allow engineers to optimise equipment design, ensure that reliability and safety are considered, and confirm operational readiness. When in a lifecycle project these studies are combined with the training of the operators, these studies can help identify any deficiencies with the DCS or safety system (interlocks and emergency shutdown systems) configuration.
It is best to use dynamic simulation to review plant startup or emergency procedures because errors there can significantly impact production. This review might take a few weeks, with additional time likely required to enhance the system. Improving the behaviour of complex systems may require some iterations.
However, it is certainly better to invest time during earlier project phases rather than during initial operations.