Estimating the duration of a project is important in project management. The dependency structure matrix has been used to estimate the duration of projects, and it has proven to be useful especially in complex projects, for example project with activity overlapping. This estimate is based on the duration of the activities, their interrelationships and the permitted level of overlap. However, these variables have uncertainty that generate uncertainty in the duration of the project. The methods of global sensitivity analysis Morris and Sobol' are used in this study to identify the key activities that affect the uncertainty in the duration of the project. It is shown that adequate control of the uncertainty in these activities significantly reduces the uncertainty in the duration of the project. Examples with and without overlapping are used to explain the methodologies.