Hey @gavin!
You will want to:
1. Create a "Users" table, where Jack and Jill would each have their own records
2. Have a linked field on your "accounts" table, linking to your new Users table (similar to what is currently doing your current "Name" field, but linked).
3. Have an automation that will trigger whenever User field on "accounts" table is not empty. The actions for the automation are (i) Find records in "Timelogs" table, where User is exactly the Record ID of the linked record under User table for the record which triggered the automation; and (ii) Update Record, to update the record that triggered the automation with the list of Record IDs found by the Find Records action.
It might sound confusing, but it is pretty simple. Just let me know if you'd like to hop on a 5 minutes call to get this solved and out of the way.
Mike, Consultant @ Automatic Nation