Abstract: The time-dependent evolution of fractures in surrounding rock of deep underground soft rock roadways directly influences the optimal timing for implementing delayed grouting reinforcement. However, the relationship between the delayed grouting timing and the time-dependent evolution of fractures remains unclear. To address the quantitative characterization of the delayed grouting timing, time-dependent borehole panoramic testing is systematically conducted to characterize the spatial distribution and the time-dependent evolution patterns of fractures. A numerical model of the delayed grouting process is established by incorporating excavation disturbance and rheological effects, and the influence of different grouting timings on roadway stability is analyzed. An optimal grouting timing determination method is proposed by comprehensively considering both the deformation and fracture evolution processes of the surrounding rock, with field validation conducted. The results indicate that the surrounding rock structure exhibits a characteristic spatial distribution of “fractured zone - fissured zone -intact zone”. The average fracture linear density shows an evolution pattern characterized by an initial rapid increase followed by stabilization. The inflection point in the growth rate of the average fracture linear density is identified as a critical temporal indicator for determining the delayed grouting timing. With the delay of grouting timing, the final deformation of the roadway shows a trend of first decreasing and then increasing. An “ optimal grouting timing” exists within the delayed grouting process that minimizes the final deformation of the surrounding rock. The upper limit of this optimal timing window is defined by the inflection point in the growth rate of displacement rate, while the lower limit is defined by the inflection point in the growth rate of average fracture linear density. Implementing grouting reinforcement within this optimal delayed timing window effectively reduces the deformation rate of the surrounding rock. In contrast, the displacement rate in roadways without timely grouting continues to increase.