Time needed for the gas disk to expand to 100 au, T_{100 au}, as a function of the infall timescale, T_infall. The size of the disk is measured at the location where the gas surface density is 1 g cm⁻². Each curve represents a different value of the initial viscosity, α₀. For each value of α₀, the orange star on the corresponding curve indicates the viscous timescale, T_visc, of the disk, to be read on the horizontal axis. T_visc represents the average viscous timescale within 10 au at t = 0 for a disk with an aspect ratio of 6%. The left panel shows T_{100 au}, and the right panel shows T_{100 au} scaled to T_infall.