Upper panel: Radius at the MB normalized to the WD radius for our 0.66 and 0.83 M_⊙ CO WD models. For the crystallization-driven dynamo models (solid lines), this radius is the outer boundary of the Rayleigh-Taylor unstable region induced by crystallization. For the main sequence dynamo models (dashed lines), this radius corresponds to the mass coordinate reached when the deepest penetration of the outer convective zone occurs in the WD progenitor evolution, either during the first or second dredge up. The filled circle indicates the crystallization onset in our models, and the empty circle indicates the time when the magnetic field breaks out to the WD surface. Lower panel: Magnetic diffusion time (t_diff) calculated using Eq. (1) for our 0.66 and 0.83 M_⊙ WD models.