Finding overlapping mm:ss within a date

I used this calculation for trunk lines at my old office. I arranged the data as thus:

A2:A9 start time
B2:B9 connection
C2: =SUMPRODUCT(($A$2:$A$9>=A2)*($A$2:$A$9+$B$2:$B$9<=A2+B2))

and copied down

Sort C Largest to smallest to find max concurrency

That's fine.

Formula logic:

=SUMPRODUCT(($A$2:$A$9>=A2)*($A$2:$A$9+$B$2:$B$9<=A2+B2))

COUNT NUMBER OF CELLS WHERE BOTH ARE TRUE:
Event begins after or at same time as event in A2
Event ends before or at same time as connection in B2

Excel saves all time and date stuff in analagous formats, such that .5 = 12 hours (12/24) and today's date is really the count of days since 1/1/1900.
Adding times together is just as easy - 11/10/2014 + 01:00:00 = 11/10/2014 1:00 AM. It's just smart like that.

So let's walk through the formula:
First expression - Which cells in A2:A9 are >= A2 (8:02:22 PM). All of them, evaluated to {TRUE;TRUE;TRUE;TRUE;TRUE;TRUE;TRUE;TRUE}
Second expression - A2:A9 + B2:B9 = {0.85400462962963;0.847326388888889;0.845497685185185;0.845497685185185;0.841863425925926;0.843888888888889;0.845162037037037;0.864722222222222}

Which of these are <= A2 + A2 (0.85400462962963)? All but the 8:43:42 PM entry which begins after the connection for A2 begins. This evaluates to {TRUE;TRUE;TRUE;TRUE;TRUE;TRUE;TRUE;FALSE}

TRUE*TRUE, TRUE*TRUE, TRUE*TRUE, TRUE*TRUE, TRUE*TRUE, TRUE*TRUE, TRUE*TRUE, TRUE*FALSE
becomes
1,1,1,1,1,1,1,0

And then it adds them up

7!