@frankatmsc Based on what you shared above, I created a project custom form and added two different calculated fields:
1. Converted Issue Entry Date (convertedOpTaskEntryDate)
2. # of Days Between Issue Entry Date and Project Actual Start Date, using your calculation from above
I then added this custom form to a project and it's working as expected, so I'm not totally sure why Customer Support mentioned you couldn't use convertedOpTaskEntryDate in a calculated field, because it works.. I even added a third column to the project report with text mode for convertedOpTask:entryDate to make sure it was correct.

With that being said, your calculation is correct for how to capture wait time. If you wanted to calculate the number of days between the date in which a request was converted to a project and the actual completion date of the project, you would swap out convertedOpTaskEntryDate with entryDate since this form is already associated with projects.
Calculated Field = IF(ISBLANK({programID}),ROUND(DATEDIFF({actualStartDate},{entryDate}),0),ROUND(DATEDIFF({actualStartDate},{entryDate}),0))
Hope that helps to clarify things!