Thank you for your post.
Instead of creating an extra site visits table, just create a relationship from Jobs into a second table occurrence of Site Visits, with the relationship set up as you described. In the Relationships diagram, click on new table occurrence, select the Site Visits table, and you will see "Site Visits 2". Set up a new relationship with Jobs and Site Visits 2 including the additional criteria "date > Get (CurrentDate)". Then, include a portal into Site Visits 2 to view the site visits that occur after today.
If you need clarification for the above steps, please let me know.