Chart axis tick labels

On charts - When bringing back data into a dataset, we have the date in column 1 (x axis) and values in column 2 (Y axis). We would like to add another level of labels to the X axis, in addition to the date ( the chart would not reference these string labels). Example: Different shift managers work the first half of the week than the second half. On the X axis we want to show the date, but also which manager was working on each date.
If our query combines the date and shift managers name the chart won’t accept it because it is not of the correct type. If we have it [manager’s name] as a different column then it errors out.
We tried having two different datasets, one with t_stamp, values, and one with names, values, and putting this second dataset on a different subplot, but the chart won’t accept that either.
Does anybody have any idea as to how to go about adding a string value (manager names) to the date labels on a chart’s x axis? Any help is greatly appreciated.