Copying wireshark-users because that's the appropriate mailing list for your question.
Have you tried using a time-based filter?
For example, you could try a filter like:
frame.time_relative > 60 &&
frame.time_relative <= 120
...to just get results for frames that showed up in the second minute of the trace you're looking at. Or you can filter on specific date/timestamps (see the "frame.time" filter). When you look at Statistics->Summary, look at the statistics for "displayed" - those are stats for packets that match your filter (
i.e. the specific time range you specified).
You might also want to look at the Statistics->IO Graphs feature, which is fairly powerful.
-Ian
