Question

Why report always shows midnight time as an interval (00:00:00 or 12:00:00 AM)?

Answer

By referring to an article of ABBYY Support Center: https://help.abbyy.com/en-us/flexicapture/12/monitoring_console/reports_processing/
the interval is: 
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As we know, each day starts from 00:00:00 and ends on the same (or 12:00:00 AM). Let's imagine the report not as a table but as a chart. Thus, the interval is a grid step (between current and previous day start).
As a day is the smallest unit in report representation, the information about FlexiCapture 12 complex performance per day (for example) is given as per the moment of the end of the day (12:00:00 AM).