Time-resolved photoinduced reflectivity is measured in the spin-density-wave phase of the itinerant antiferromagnet UPtGa5. Two relaxation components were seen: (a) a slow component whose amplitude appears below TN, and relaxation time τslow exhibits an upturn near TN, and (b) the fast component persists at all temperatures, with the relaxation time τfast also exhibiting an upturn near TN. Comparing with pump-probe data on UNiGa5, the differences are explained in the context of UPtGa5 having A-type (rather than G-type) antiferromagnetism, resulting in partial Fermi surface nesting, partial gapping, and consequently finite density of states at the Fermi surface.