Calculate How Many People Are Working At The Same Time using the COUNTIFS Function

I'm trying to utilize the COUNTIFS function to see how often certain meeting rooms are being used throughout the day. I found an example online (noob, can't post link yet but it's from howtoexcelatexcel) that uses number of employees working, but I think I should be able to use it:


However, I can't get that example to work - the "Working Hours" on my sample always equals zero. I even tried making a copy of their example, and I'm still getting zeros. If someone could let me know what I'm getting wrong I'd appreciate it.