Just as long as you remove all the voltage from the cells entirely there shouldn't be anything wrong with leaving them for a week. The other method will work fine too, but be sure that there is a bit of charge left when you store them for a week. Discharge the cells as much as possibe before putting them on the tray. It is very important that you don't put charged cells on the tray. The pressure will build inside the cell and pretty soon they will vent to release the pressure, damaging the integrity of the cell.