Predicted evolution of the g-mode cavity rotation frequency as a function of the hydrogen-mass fraction in the core for different initial rotation frequencies as a fraction of the initial Keplerian critical break-up frequency. In each panel, the stellar mass and f_ov correspond to those in the best-matching model listed in Table 2. The black markers indicate the observations, where the X_c estimate is from this work, and the rotation frequency is from Li et al. (2019, uncertainties on Ω_gc smaller than symbol size). The solid lines are models with a constant uniform viscosity (Sect. 3.1), whereas the dashed-dotted lines are the models with rotational instabilities (Sect. 3.2).