This paper presents the ways of quantification of flow time qualifications that can be used for planning or other stochastic processes by employing Clark’s methods, central limit theorem and Monte Carlo simulation. The results of theoretical researches on superponed flow time quantification for complex activities and events flow in PERT network for project management are also presented. By extending Clark's research we have made a generalization of flow models for parallel and ordinal activities and events and specifically for their critical and subcritical paths. This can prevent planning errors and decrease the project realization risk. The software solution is based on Clark's equations and Monte Carlo simulation. The numerical experiment is conducted using Mathcad Professional.