Copyright 2016 Society for Modeling & Simulation International (SCS).High performance computing (HPC) has great potential to speedup agent-based simulations. In parallel and distributed simulation (PADS) community, a well-known fact is that employing an optimistic time management mechanism instead of a conservative time management mechanism may provide remarkable performance enhancement, because optimistic approach avoids redundant synchronization among logical processes (LPs). In this paper, an existing optimistic time management mechanism, namely Time Warp, by Jefferson, is adapted for a distributed agent based simulation tool. We implemented Time Warp on an open source and distributed agent based modeling and simulation (ABMS) tool, namely Repast for High Performance Computing (Repast HPC), from Argonne National Laboratory, Chicago, IL, USA. We incorporated a simple and self-adaptive technique for adjusting checkpoint intervals. Two case studies have been implemented to compare our optimistic approach and existing Repast HPC's conservative approach. The experiments suggest that optimistic approach is more scalable than conservative approach in agent based simulations.