Anthony,
It looks like we currently only consider the columns/fields from the base query/dataset when providing a list of available dimension options for the time chart.

However, I believe that you can create your desired chart using the following steps:
1. create a custom query over your base copied-to-study assay dataset in the study (see attached query example using a NAb assay)
2. write the query so that it includes the Primary/Derivative fields you want to use plus the measures you want to plot from the assay dataset
3. create a Time Chart over that custom query
4. if the Primary/Derivative columns don't show up as available dimensions, go back to your query and edit the metadata to set those fields as data dimensions

Give that a try and let me know if it does not work for your scenario.
Thanks,
-Cory