Public participation has long occupied a central position within planning and design theory. From Arnstein’s seminal work on citizen participation to collaborative planning, co-production, and contemporary participatory design approaches, scholars and practitioners have increasingly recognized the importance of involving citizens and users in shaping urban environments. Despite these advances, participation continues to be understood predominantly as an episodic and project-based activity associated with specific interventions, workshops, or consultation processes. Relatively limited attention has been devoted to the temporal dimensions of participation and to how users, places, meanings, and needs evolve over time. This study argues that time remains one of the least-explored dimensions of participatory planning and design. Building on literature from planning theory, participatory design, commons scholarship, care studies, and emerging work on temporality, the study proposes participatory temporal urbanism as a conceptual framework for understanding participation as an ongoing and evolving relationship rather than as a discrete event. The framework introduces five interrelated dimensions: co-creation, deliberation, co-management, co-adaptation, and co-memory. Drawing on concepts such as stewardship, commoning, maintenance, and care, the study further argues that sustainable urban development requires forms of participation that extend beyond implementation and continue throughout the life cycle of places. Particular attention is given to deliberative approaches, including the jury principle associated with New Urbanism, and to the role of participatory design in accommodating changing social, cultural, and intergenerational needs. By introducing time as a central analytical category, the study contributes to ongoing debates on participatory planning and participatory design and offers a new framework for understanding the collective processes through which sustainable cities can be collectively shaped, maintained, and continuously reinterpreted over time.