Surface ¹⁴N abundance as a function of stellar age of our model 20 M_⊙ star with initial equatorial rotational velocity of 300 km s^-1. Model sequences are run with fixed shell mass δm = 0.05 M_⊙ with different timesteps δt. These model sequences are run with BONNFIRES using the implicit scheme for calculating diffusion coefficients, as described in Sect. 2. We note that deviations of surface abundances may fluctuate non-monotonically, for example, the model sequence with δt = 0.05 Myr has slightly lower surface ¹⁴N abundances than sequences with smaller timesteps.