Calculating times when the end time could be before the start time

I am so lost and I have read so many forums. Is anybody able to help me?

Basically, I am tracking the performance of a live production line. New dates and times are sent out twice a day every day. I need to track if the new loading times are going forward or backward. Of course the forward times are easy, I've read many forums but can't seem to narrow down how to read the negative value in hours as shown. The cell will need to read either the positive or negative value depending on the next updated schedule sent out. Please see attached picture for reference.

Thanks so much