I'mnot sure if your employees table has a table �above it� such as company or branch or division, so I will assume not. If you do that that you can follow my steps below without needing the extra dummy table.
Make a dummy table called employee counts and add one record. It will be Record ID of 1.
Make a relationship to the time cards table and for the reference field, change that related employee counts field to be a formula numeric that calculates to be a 1.
Then using the new feature, maybe a summary count distinct summary field on time cards to count distict on employee name or employee ID #. Limit that to where Date is during the current month. Call that field EE count CM.
Duplicate that field and adjust the date range to during 5e previous month. Call it EE count CM-1.
Duplicate that field and adjust the date Range filter to during the previous 2 months and not during the previous 1 month.
Call it EE count CM-2.
Just keep making Making summary fields until you get say 13 of them for the current month and past 12.
