Top: χ² metric (orange curve) as a function of the simulation time t. The thick dashed line shows the evolution of N_box, and the thin dashed lines are 1-σ and 3- σ confidence levels, the latter of which determines the interval of relevant ages of the family (light blue rectangle). The minimal ratio χ²∕N_box is attained at t = 281 Myr. Bottom: a box-by-box map of the χ² values at t = 281 Myr. The displayed (a_p, e_p) plane corresponds to the inclination range sini_p ∈ (0.43;0.453). Black points and blue crosses are synthetic and observed asteroids, respectively.