HR diagram for stars between 16 and 28 M_⊙ with convective cores reduced by the same factor, f = 1.18. Time steps for every 10⁵ years are shown as small circles, starting at the end of the main sequence for clarity. The location of known massive magnetic main sequence stars (Briquet et al. 2013; Petit et al. 2013, and references therein; Alecian et al. 2014; Fossati et al. 2014; 2015; Neiner et al. 2014; Castro et al. 2015) are shown as yellow dots. Additionally, we draw the zero age and terminal age main sequences of the non-rotating models of Brott et al. (2011) as dashed lines.