Calculating An Average But Excluding Boxes With Text

I'm trying to get excel to calculate the average time spent on appointments by officers in a small team. Each of them sees people each day, and as we're very busy I'm eager to get the time spent on each appointment down, by giving them a target of the number of people to see each day. At the moment we gather some stats on this, which show how many people are being seen by each officer.

The attached example sheet shows for one week a list of columns with officer's initials at the top, and says how many people were seen by each person each day during that week and then a how many people overall for the week.

I'd like to be able to generate statistics on the amount of time each officer has spent on average with customers, and base this on the fact that people have 360 minutes per day (they do 6 hours of appointments and another hour for admin) to see people.

I think the spreadsheet attached gives a good idea of the system and what I want to do.