Planners, your thoughts on this please!

I am trying to compare original duration with actual duration of a project.

Original Duration (OD) is how long estimated for an activity to start and finish and does not in any way represent the Actual Duration (AD) it took for the same activity to start and finish. P3.1 does not have a feature (at least to the best of my knowledge) that calculates AD, hence AD can be calculated manually by exporting P3.1 data to excel and manipulating data as;

Theory:
Actual Finish Date minus Actual Start Date equals Actual Duration (in days)

Now consider the scenario below:
1. Planning unit is in hours
2. Calendar working hours equals 16 hours (day shift & night shift – 8 hours per shift)
3. Activity Id, % Progress, Actual start date (date only, no time), & Actual finish date (date only, no time) is imported into P3.1 via excel.
4. There are separate fields in P3.1 for date in the format dd/mm/yyyy and time in the format 00:00

Further illustration:
A. If an activity starts 7am 6th July and finishes 7pm 6th July (day shift), then AD = 0 day (because only dates are imported into P3.1).

B. If an activity starts 7pm 6th July and finishes 7am 7th July (night shift), then AD = 1 day (because only dates are imported into P3.1).

C. If an activity starts 7am 6th July and finishes 7am 7th July (day shift), then AD = 1 day (because only dates are imported into P3.1).

The closest I can get is replacing 0 & 1 with the calendar duration of 8 hours; however, only dates are imported into P3.1, I have no way of differentiating B & C above, and also an activity could start and finish within 4 hours of the start of the shift, hence doing that will be erroneous.

It appears the ONLY real way of doing this would be reporting actual start date & time of each activity in the project. If the latter is the case, then how can I format the date field and the time field in the format m/d/yy h:mm so that it can be used for my analysis.

I hope I have explained this very well. Your special thoughts please!