The other approach which will work if you do not have simultaneous users of the chart at the same time is to create an admin record in a single record table with record id =1.
then you make. Formula URL button to populate the value of the reference date into that record. Then lookup that value down to all details cords. Then have. Formula in details that calculate es to true if the date is with the plus minus 28 day range.
This can be enhanced further using the user focus method to allow for simultaneous users.
so the concept is that the charts are not initially exposed. The user click the button and puts the parent record in focus by writing its record id# and the reference date into that admin record.
Then the record is refreshed during that same URL button click and form rules now display the chart.
Feel free to contact me if you need one on one assistance t9 getting this set up. It will take under an hour of consulting time. Maybe 30 Minutes. mark.shnier@gmail.com