Maximum solid density evolution as a function of time comparing the effect of the time of gas removal, such that the gas density is halved every 50 or 100 orbits, respectively. Here, q = 3.5, τ_s = 10⁻³–10⁻¹ and both systems have N_p = 7 particles per cell. The dashed line corresponds to ρ_p,max∕ρ_g = 100, which represents the critical maximum solid density needed for filament formation. There is a difference of about 0.02 in the critical metallicity, depending on the gas removal time.