 Radiative mass loss at fixed luminosity

For luminosity $L$, mass-energy equivalence gives $|\dot{M}|=L/c^2$. Holding $L$ constant gives a time $t=fM{c}^2/L$ to radiate a mass fraction $f$. A blackbody estimate uses the Stefan–Boltzmann law, $L=4\pi R^2\sigma T^4$. This is a radiative-energy estimate, not a model of a star's evolving nuclear fuel or mass loss in a wind.