figure out the maximum amount of concurrent calls

Hi,
My goal is to figure out the maximum amount of simultaneous calls at any given time. Basically, if there are 5 people on the phones at 9:38am for example, I need "5" as a result; if there are 3 on the phones at 1:21pm, for example, I need it to return 3. After the calculations are done, then I need to put the highest number, like the maximum amount of people on the phones at any given time. We are trying to figure out how many trunks we need to purchase and must avoid anyone getting a busy signal. If the maximum is 4, for example, we will purchase 4, in turn will allow a maximum of 4 people on the phones concurrently without an inbound call getting a busy signal.

Also, your latest worksheet, I am having trouble finding the formula for it turning a different color. I have attached a months view of the calls I am trying to figure out. Hopefully you may plug that formula in at the top and I can do the rest.

Thank you for all of your wonderful help and expertise!