Action immediately, if necessary. Hoping that a problem will go away without corrective intervention is naïve. Based on actual progress, it is possible to forecast a schedule and budget for completion of the project. If these parameters are beyond the limits of the project objective, corrective actions need to be implemented at once.
Attempting to perform a project without first establishing a baseline plan is foolhardy. It is like starting a vacation without a roadmap, itinerary and budget. You may land up in the middle of nowhere-out of money and our of time!