Evolution on the HRD for t < t₀ for both metallicities Z = 1 Z_⊙ (solid lines) and Z = 0.2 Z_⊙ (dashed lines). The values at time t = 0 Myr (t = 2 Myr) are marked with circles (triangles) and the yellow, red, and blue lines show models with Ṁ_start = [1 × 10⁻⁹, 5 × 10⁻⁹, and 1 × 10⁻⁸] M_⊙ yr⁻¹, respectively. The onset of deuterium burning (t = τ_D) is marked with a diamond. The transition from expansion toward the Hayashi track (t = τ_H) is marked with a cross.