Time is money is the natural approach for managing any project.
For contractors project finish delay usually means an increase of project expenses, for owners/investors project finish delay means that profits will be get later and so some profit will be lost. The cost of time is different for different project participants and yes, for some of them it is not easy to calculate accurately the cost of delays.
When project starts it is necessary to define project success criterion. Usually there are a lot of them (triple constraint as an example) and it makes project decision making subjective. Is it right to pay $10000 more but to finish the project one week earlier? Or select the subcontractor that costs $ 50000 less but to finish project three weeks later? Without estimating the cost of time these decisions cannot be justified. So it is necessary to set one integrated project success criterion that provides certain answers to above questions. Yes, cost of time estimates may be not accurate but they shall be known by project managers for future decision making and approved by project sponsors. It refers not only to cost but to any other value created by the project. These estimates are usually done not by project managers but shall be provided to project managers by top management (sponsor, PMO, CFO) in the Project Charter.
Contractors do not model future profits but shall include in the project model the cost of time and potential penalties and rewards.
Investors shall model future profits, so their models shall include post project completion periods. At project gates the decisions how and if to proceed are based on overall expected project results. When uncertainty is high risk simulation is required and we will discuss the problems with Monte Carlo simulation in the separate thread.
An example of the project where both expenses and profits are modeled is included in Spider Demo. At the picture below Gantt Chart of similar project is shown.
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