If you use FEFLOW 6.0 and if you want to assign time-dependent material properties you have to use the old GUI. You may open the old GUI if you click on FEFLOW Classic in the Start menu. The Qt version (FEFLOW standard) does not allow the assignment of time-dependent material properties.
From the functionality point of View FEFLOW 6.0 can be considered as a transition state between the old (classical) GUI using MOTIF and a new GUI using Qt. At this time not all functionalities from the old GUI have been transferred to the new GUI. This is also the case for the assignment of time-dependent material properties as such as the groundwater recharge.