The emission time extracted from two-particle relative-momentum correlation functions has been studied as a function of the spatial extent of the source for 40Ar+197Au reaction at 25MeV/u.Reduction of ～50% in the mass number of the source has a very small effect on the calculated correlation functions and the extracted emission time.For the cases of short emission time τ(τ≤100fm/c),use of a smaller nuclear density would lead to somewhat smaller assignment for τ;therefore,these τ values extracted in the normal nuclear density can be taken as upper limits of τ values.For the cases of long emission time (τ≥300fm/c),the emission times do not vary with the size of the source and these τ values can be taken as the real values.