Duration of PMI

I’ve seen PMI process that last for extensive period, with other being much concise. While I understand that the duration of PMI process would depend on case by case and magnitude of issues to be dealt with, what is your experience in general with the duration of intensive PMI task engagement (weekly calls, task team hours, etc.). I am asking since once these tasks start, there continues to arise further tasks which seems to make PMI process a never ending one… (though I am aware that setting a clear KPI to achieve certain level at certain time period should address this issue; but that also depends on the appetite of the one who leads the PMI…). Trying to understand what everyone’s experiences and advice would be.