This calculated field will display the difference between two dates reflected in Date picker fields in business days.
Name the calendar with a recognizable name as in the following example.
Business Hours
Introduce a relevant expression in the Specification field like the following one:
MON-FRI{09:00-17:00;}
Create a new Calculated Text Field (by JWT) custom field and name it properly.
Providing a description will help you to identify what the custom field does but this step is optional
Add the following parser expression:
formatWorkDuration(timeDifference({issue.cfaaaaa},{issue.cfbbbbb},"Business Hours",LOCAL))
Add the field to the relevant view screens.
Remember: All calculated fields are read-only and cannot be manually updated on a create or edit screen.