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Probabilistic time estimation is an essential part of proper risk management in tunneling projects. In recent decades, several models have been developed for this purpose, one of which was developed by Isaksson and Stille (Rock Mech Rock Eng 38:373–398, 2005). In this paper, Isaksson and Stille's probabilistic time and cost estimation model was improved and then applied to estimate the total tunneling time of the headrace tunnel in the Uri hydropower project in India. The improvements allow the user to more accurately account for different types of geological features and disruptive events. The result of the estimation is a distribution of tunneling time. The outcome illustrates how a proper understanding of the geological setting of the project and its effect on construction performance can contribute to effective risk management. Highlights: The application process of an existing model for probabilistic time and cost estimation of tunneling projects was improved. The improved model was used for time estimation in a case study to demonstrate its application. The outcome of the model application is a mixture distribution of total tunneling time. Further discussion is put forward on the general modeling considerations, the shape of the mixture distribution, and application of the model in tunnels with multiple excavation faces. [ABSTRACT FROM AUTHOR]