Coulomb potential may induce a significant angular offset to the two-dimensional photoelectron momentum distributions for atoms subject to strong elliptically polarized laser fields. In the attoclock experiment, this offset usually cannot be easily disentangled from the contribution of tunneling delay and poses a main obstacle to the precise measurement of tunneling delay. Based on semiclassical calculations, here, we propose a method to extract the equivalent temporal offset induced solely by Coulomb potential (TOCP) in an attoclock experiment. Our calculations indicate that, at constant laser intensity, the TOCP shows distinctive wavelength dependence laws for different model atoms, and the ratio of the target atom’s TOCP to that of H becomes insensitive to wavelength and linearly proportional to (2I_p) ^3/2, where I_p is the ionization potential of the target atom. This wavelength and I_p dependence of TOCP can be further applied to extract the Coulomb potential influence. Our work paves the way for an accurate measurement of the tunneling delay in the tunneling ionization of atoms subject to intense elliptically polarized laser fields.