Program estimation for TBM drives is a critical task to perform in the engineering phase, because costs and planning are based according to this prediction. Several tools are available including empirical and semi-theoretical models. During construction, they still can be used due to rock mass information that is coming from the excavation process, which allows for constant update and planning. For the construction of the Safety Gallery of the Frejus Tunnel, driven by a Single Shield TBM, a methodology was applied considering two prediction models, Colorado School of Mines and Norwegian University of Science and Technology at Trondheim, to predict cutting speed and advance rate for different rock masses considered in the layout. Additionally, a Monte Carlo simulation was applied to know the variability of those. As a final result, three main scenarios were obtained (Conservative, Average and Optimistic) for the total excavation time, giving a reliable frame for the expected TBM drive. This methodology is intended to serve as a general procedure for any TBM project, to evaluate in a rational way geological uncertainties.