Many Lagrangian models require knowledge of the integral time scale of the fluid on the discrete particle trajectory. This characteristic of the fluid seen cannot be readily observed experimentally. Three models to assess the integral time scale of the fluid seen in a homogeneous isotropic turbulent flow have been found in the literature. This work aims to investigate the efficiency of these models in reproducing the three main effects, i.e., inertia, crossing trajectory, and continuity effects, by comparison with the experimental data obtained in an isotropic, grid-generated turbulence. The main results of this study show that the inertia effect is better reproduced using Wang and Stock's (1993) relation. When both inertia and crossing trajectory effects are present, Pozorski and Minier's (1998) expressions are recommended. Derevich's (2000) method did not give satisfactory results, and it could not take into account the continuity effect.