I tried putting -1 and 0 for Job Display Duration and tried posting new jobs. Below is the result.
The Closing Date field does not appear while creating a new job post. However, the calculated closing date based on previous value of Job Display Duration(90 days) appears in all the places listed below
1. On Jobs page in job listing summary
2. On Single Job Page
3. In Employer Dashboard - Manage Jobs section
4. In Admin WordPress dashboard
It is very important to apply this setting to the existing users who have purchased this package.
regards
hemant