Using reports to total time

[LBitner99]

I have a table that records specific "timestamps" of when a certain product reaches specified points in production. i have generated a report that can calculate the total time lets say "BoB" spent on a specific serial #. the issue is that if bob looks a serial # in "assembly" at 12:48 and then stamps it going to "programming" at 12:50 but then adds a record again for the "done" stage at 15:40, it records over 3 hours of time, because i have the report taking the first and the last times and calculating the difference.

Does anyone have any idea on how to get the report to tell when to and when NOT to include a record in the calculation? mind you this HAS to be done form the query and report levels, the table CANNOT be changed. Any help would be a lifesaver!