To do Frequency by time graphs, select the channel and then select the frequency in the measurements dropdown box.
Settings | Input Channels | OK | ADD or Edit
In the window there is a scan time which determines the frequencies that can be read. This is described under the box and will change as the scan time is changed.
Select a data file that the data will be saved into and start a run the frequency will the be seen in the graph.
I have tested this with Picolog release 5.09.4.