A small sample of a coal slurry containing particles with equivalent spherical diameters from 1 to $500 \mu \mathrm{m}$ is introduced at the top of a water column $30 \mathrm{~cm}$ high. The particles that fall to the bottom are continuously collected and weighed to determine the particle size distribution in the slurry. If the solid SG is 1.4 and the water viscosity is $1 \mathrm{cP}$, over what time range must the data be obtained in order to collect and weigh all of the particles in the sample?