Hi,

in your original post you wrote
My phone system can handle 24 concurrent calls. I'm trying to see how many times throughout the month did we have 24 or more calls going on at once.
So, as I said above, althoug one single long call may during its duration overlap with 24 other calls, it may still be that these 24 calls are not active at the same time. You really want to see if 24 calls went on at the same time, which is not the same as overlapping with the current call.

See the difference?