The choice of flowback timing has a significant impact on the flowback productivity effect, flowback rate, and water saturation. This paper studies the imbibition mechanism and migration variation of fracturing fluid through analyzing the phenomena of spontaneous imbibition experiments and dynamic/static experiments. Starting from the core scale and mine field scale, numerical models such as geological models, fracturing fluid flowback models for natural closure and forced closure processes, horizontal well fracturing productivity models, and shutdown time optimization models are established. These models are used to solve for the optimal shutdown time and analyze various influencing factors. The results show that during the shutdown process, the fracturing fluid enters the core and undergoes imbibition displacement, promoting the generation of new micro-fractures, thus improving the recovery rate. The calculation of a reasonable shutdown time has a positive impact on the physical property variation characteristics of the reservoir, the diffusion degree of wellhead pressure, the peak production capacity, and the effect of imbibition displacement equilibrium. The determination of the optimal shutdown time provides good reference for on-site flowback operations and improving the flowback rate.