Stellar tracks for stars with mass M = 40,  50, and 60 M_⊙ at Z = 0.002 (upper panels) and Z = 0.004 (lower panels), encompassing the metallicity range of the SMC. Columns represents different initial rotations: Ω = 0 (left), Ω/Ω_c = 0.3 (middle), Ω/Ω_c = 0.6 (right), corresponding to the minimum, average, and maximum observed rotation velocities of O-type stars in the SMC. The color code shows the time spent in different regions of the HR diagram τ_HRD.