In recent years, time synchronization in Wireless Sensor Networks (WSN) is important for accurate time stamping of events and fine-tuned coordination of duty cycles to minimize power consumption. This paper presents an On-demand Hierarchical Mesh-based Time Synchronization (OHMTS) that is flexible, multihop based and high-precise in WSN. OHMTS adopts hierarchical and multi-hop mesh-based network architecture with supporting energy-saving problem for WSN. For the purpose of performance evaluation, we first study the error sources of OHMTS and then we evaluate the performance of OHMTS with respect to synchronization delay error using network simulator (NS-2). The simulation results show that OHMTS provides fine-tuned clock offset mechanism and can be easily applied to real WSN platform.