[HM] small correction on staggered scheme benchmark

A further review revealed a discrepancy between the time scale of the results with the reference [Kim]. Indeed, the time nondimensional time refers to the pore space filled and not the full domain. Thus the reference time was corrected from 1500 days to 450 days. In addition the exact value for the permeability unit Darcy is now used instead of the approximation of 1mD=1e-15.