Time synchronization has always been a critical deciding factor of whether interoperating simulation models using the High Level Architecture (HLA) is achievable efficiently. In this paper, we propose a conservative time synchronization algorithm that makes use of the manufacturing process flow information (a sequence of steps production lots flow through) in the computation of the request time. This time is used by the simulation federate to issue requests to advance time to the HLA Runtime Infrastructure (RTI). The proposed algorithm monitors the simulation events that potentially trigger external timestamp messages at the exit step and j processing steps before this exit step as well as simulation events that extend the timestamp of external messages. We evaluated the performance of this algorithm using a Borderless Fab simulation model on the AutoSched AP. The experimental results show that the algorithm performs much better than a straightforward use of the RTI?s time synchronization, and the further back we went in looking at the processing steps, the better the execution time that was achieved.