Different characteristic timescales as a function of the accreted mass: winding (black), Tayler instability (dark blue), and dynamo (red). The green line represents the sum of the three timescales. The shear rate is set at q = 1. The green crosses represent the entire amplification time obtained by integrating Eqs. (37)–(39). The red vertical line shows the lower limit of the accreted mass to form a magnetar with a radial field stronger than B_Q ≡ m_ec²/eℏ≃4.4 × 10¹³ G using the predictions of Fuller et al. (2019).