The article deals with the practices of how to estimate pessimistic scenarios of construction tasks duration which are based on latent regularities of space-time and space-cost analogies. It is presented herein that planned values of tasks duration are sufficient to be used for optimistic scenarios development. But in case of pessimistic duration it is necessary to consider planned durations and starting points of work tasks, as well as such a discount rate which is used to estimate economic efficiency of an investment construction project under study.