Quantum time synchronization is an interdisciplinary frontier technology that integrates quantum technology with time-frequency technology. By leveraging the intrinsic nonlocal time correlation of frequency-entangled biphoton sources, two-way quantum time synchronization not only improves the precision of existing time synchronization by 1～2 orders of magnitude but also possesses inherent security advantages. This provides a new generation of transformative technical solutions for significantly enhancing time service precision and ensuring time service security. This paper focuses on the research progress achieved by the National Time Service Center of the Chinese Academy of Sciences in the field of two-way quantum time synchronization: a model for evaluating the accuracy of two-way quantum time synchronization has been established; the first international demonstration of 10-femtosecond-level ultra-high-precision quantum time synchronization was reported; successful demonstrations of sub-picosecond-level time transfer were achieved on a 2 km free-space + 7 km field fiber hybrid link, hundred-kilometer field fiber link, and a 250 km ultra-long-distance fiber link, fully validating the high-precision synchronization ability of this technology under high-loss and strong-noise environmental conditions; meanwhile, the security advantages of the quantum time transfer system have been experimentally verified. These research achievements not only mark significant progress in the field of long-distance fiber-based quantum secure time transfer in China but also provide a highly compatible time synchronization solution for the future construction of large-scale quantum networks.