In this paper we analyze the interval availability of a two-echelon, multi-item system. Modeling the system as a Markov chain we analyze the interval availability of the system. We compute in closed and exact form the expectation and, the variance of the availability during a finite time interval [0,T]. We use these characteristics together with the probability that interval availability is equal to one to approximate the survival function using a Beta distribution. Comparison of our approximation with simulation shows excellent accuracy, especially for points that are practically most relevant.