Crystal Reports Grouping records within the same time frame

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     Good day all! I'm hoping someone out there can really help me figure this report out!!  Here's the jist;

We use Cisco Call Manager for our VoIP telephone system, and with Call Manager, there is a database assigned to it for the Call Detail Records (CDR).

I am being asked to comprise a report that shows my management staff when our max concurrent calls are reached throughout the day, within a given time frame of dates (So, say, for the last 120 days).  PArdon me if I'm not making sense yet, hopefully I can explain it by the end.

So, basically, the CDR database will hold all the info on the calls incoming and outgoing, dates and times, duration, yadda, yadda for each call - What I need to be able to show is how many calls werer happening AT THE SAME TIME.  The hard part is though, that the calls obviously don't need to start and / or end at the same time, just have happened within the same period of time.

For example - I have Call #1:
Call started at 12:03PM and ended at 12:56PM

Call#2:
Call started at 12:25PM and ended at 1:10PM

Call #3:
Call started at 1:00PM and ended 1:15PM

So, all 3 of these calls were going on within the same period of time at some point.  What I need to do is group the records that happen together and group it by hour and show an average count of concurrent calls within that hour.

Btw, I'm a novice at Crystal Reports!

Any help will be GREATLY appreciated!