The safe estimation of a duration during the planning of the Project Management schedules is a key objective for Project Managers. However, linear approaches fail to include and sufficiently serve the dynamic nature of many characteristics of an activity. The present research emphasizes in designing and implementing a methodology that approximates the duration of the activities during the phase of planning and scheduling, utilizing Grey Analysis mathematical modeling and comparing it to linear methodologies. These tools are based on time series analysis, which includes prior knowledge and experience that are taken into account during the duration estimation process. By adopting the aforementioned procedure, a Project Manager is able to provide duration approximations that fit reality better. In this book, the proposed procedure contributes to the decrease of the uncertainty concerning project completion time. Under some presumptions, the proposed methodology can be applied to any type of project and reduce, up to a scale, inaccurate estimations of Project Managers. The survey concludes with a bridge case study that validates its effective use.