Number Of Staff In Building At Particular Date / Time

I have data showing when staff arrive at, enter after clearing security and then exit a building after completing their task. The data for each cell is a combined date and time as opposed to separate cells for date and time.

I am trying to ascertain how long our security staff take to clear persons waiting to enter the building and also how many people at any one time are actually in the building (after being processed through security).

I also need to ascertain if particular issues arise at certain days of the week (eg Mon morning) and so need to add a further column which shows the day of week using the date/time data.

A sample of the data is as follows;

Staff No:
Arrival time
Processed time
Exit time

1
26/02/2013 07:13
26/02/2013 07:22
26/02/2013 13:52

[Code] ........

I had thought about trying to display the data using a a stacked bar chart but I still need to look at any particular date/time and ascertain how many persons are in the building without manually counting the rows!