The time needed (time-lag) for aerosols and hydrosols to reach the self-preserving state by coagulation is investigated. A discrete-sectional model is used to calculate new, accurate, self-preserving distributions in the free-molecular and continuum regimes. Correlations for the corresponding time-lags for arbitrary broad, initially log-normal distributions are presented in dimensionless form and compared with literature data. Practical applications are given indicating that industrial aerosols rapidly attain the self-preserving state.