Time-resolved photoinduced reflectivity data were measured for the itinerant antiferromagnet UNiGa5 (TN
≈ 85 K) from room temperature down to 10 K. The relaxation time τ increases sharply near TN
, which we attribute to the opening of a spin gap. In addition, at the lowest temperatures τ increases with a T1
dependence, which is similar to that shown by the heavy fermion YbAgCu4, but with no blocking of electron-phonon scattering within the DOS peak. The transient amplitude increase at TN
with a temperature dependence that is consistent with the appearance of a spin gap.