Fractional MS τ-distributions of a) the magnetic stars and b) all stars in our sample. Panel c) shows the fraction of magnetic stars as a function of fractional MS age, normalised such that the incidence of magnetic stars is 7% (Wade et al. 2014; Fossati et al. 2015b). The shaded regions indicate bootstrapped 1σ estimates to give an indication of the statistical significance of the variability in the τ-distributions. The solid line in the middle panel shows the τ-distribution of our synthetic population of a magnitude-limited sample of massive stars (see text).