24hr Timing issue

Hi, i really hope someone can help me with this problem. I'm ok with excel formulas, but damn this problem has been doing my head in for a few days now.

anyway, i have a huge spreadsheet with individuals arrival date and time (A2) and leaving date and time (B2). These date and time entries are in the format: "dd/mm/yyyy hh:mm".

Ultimately i need to show how many are in attendance at any given day and time. I have decided the best way to do this is to have hour slots (columns) and then have a formula to simply insert a "1" in each and every hour slot that the case was present until leaving. this works fine, until the person leaves the next day - i cannot get the formula to handle the 24hr time!.

To give you and idea of the ideal ultimate outcome - what i am eventually wanting to do is plot on a chart the busiest hours. I have thousands of row entries of arrival and leaving times going back a couple of years.

i have attached a simple cut down version of the problem. Any help is appreciated.