Diurnal rhythms, the natural 24-h cycles of light and darkness, significantly influence the timing and regulation of cell division, a vital process in plant growth and development. Plants precisely synchronize their cell division cycles with these rhythms to maximize energy utilization, synchronize growth, and adapt to environmental changes. A crucial function of the circadian clock is regulating cell division phases, namely the shift between the G1, S, G2, and M phases. Environmental cues such as light and temperature serve as external signals that interact with internal molecular pathways to control the speed and timing of cell division. The present chapter delves into the impact of daily rhythms on the molecular processes of cell division in plants, encompassing the involvement of cyclins, cyclin-dependent kinases (CDKs), and other cell cycle regulators. Furthermore, it explores these rhythms’ impact on plant growth rates, tissue differentiation, and developmental processes. Moreover, the chapter emphasizes the need to comprehend diurnal regulation in agricultural practices, namely in optimizing growth cycles and improving crop stress resilience.