This study discusses sustainable design strategies for Japanese public libraries by introducing the time concept. Currently, public libraries in Japan are facing declining utilization and decaying facilities, and many require renovation or reconstruction. We explore how design can help libraries avoid their current dilemmas and cope with the increasing e-books and pandemic-born boom in online learning and communication. Only by addressing these issues and planning for similar situations in the future will libraries manage to achieve their sustainability goals. This requires a systematic rethinking of traditional library design approaches by introducing the time element. We review the development of Japanese public libraries to identify the short- and long-term roles of libraries in cities from an international perspective, based on which we reevaluate the functions of public libraries. As different regions and conceptions of time and space influence people's needs for space and services, we also explore the view of time in architecture and the unique Japanese time perception. We then discuss possible solutions for libraries in Japan and the feasibility for other countries.We have three main suggestions. 1. A central + local development model.2. A three-stage design process from stable to resilient.3. An operating plan considering the economy.