FEFLOW can calculate the drawdown by time, for example, the Hydraulic head at time step 0 minus the Hydraulic head at the current time-step in the following way:
Step #01 - In a .fem file, create a Nodal expression in the User Data Panel - see Fig. 1
Fig. 1 - How to add Nodal Expressions
Step #02 - Rename it, then open the Expression Editor by right-clicking and selecting "Edit Parameter Expression..." - see Fig. 2
Fig. 2 - Edit the Expression
Step #03 - Define the expression corresponding to the formula Head @(0)-Head - see Fig. 3
Fig. 3 - Expression editor
Step #04 - Run the .fem file after you specified the result file name and folder. Open the .dac file just generated, and you will get to see the results of the drawdown by double-clicking on the Nodal Expression created above, in the Data panel - see Fig. 4
Fig. 4 - The results of the Drawdown calculation