In this paper, we propose an approach to the reliability analysis of distributed programs that addresses real time constraints. Our approach is based on a model for evaluating transmission time, which allows us to find the time needed to complete execution of the program, task, or mission under evaluation. With information on time constraints, the corresponding Markov state space can then be defined for reliability computation. To speed up the evaluation process and reduce the size of the Markov state space, several dynamic reliability preserving reductions are developed. A simple distributed real time system is used as an example to illustrate the feasibility and uniqueness of the proposed approach.