[en] Core-collapse supernovae emit of order 10⁵⁸ neutrinos and antineutrinos of all flavors over several seconds, with average energies of 10-25 MeV. In the Sudbury Neutrino Observatory (SNO), a future Galactic supernova at a distance of 10 kpc would cause several hundred events. The v_μ and v_τ neutrinos and antineutrinos are of particular interest, as a test of the supernova mechanism. In addition, it is possible to measure or limit their masses by their delay (determined from neutral-current events) relative to the v_e neutrinos (determined from charged current events). Numerical results are presented for such a future supernova as senn in SNO. Under reasonable assumptions, and in the presence of the expected counting statistics, a v_μ or v_τ mass down to about 30 eV can be simply and robustly determined. This seems to be the best technique for direct measurement of these masses. (Author)