Various applications and services have been provided over broadband optical access networks such as passive optical networks (PONs). The data communication among optical network units (ONUs) in the same PON, i.e. inter-ONU communication, is expected to be one of the most attractive communication architectures in the future, since it can provide low-latency peer-to-peer (P2P) communication services. However, the current PON systems cannot provide the services which require precise time synchronization among ONUs, e.g. smart grid services. This paper proposes an inter-ONU time synchronization technique using jitter buffer in the optical line terminal (OLT) to make inter-arrival time of control messages for time synchronization a constant value. The practical effectiveness of the jitter compensation technique is verified by a numerical simulation. The simulation results show that the proposed technique provides small packet delay variation (PDV) of the control messages, and improves the synchronization accuracy.