BBF and exposure

[PhotoriousMe]

Recently I set my D7200 to use back button focus. My question is when I depress the AE-L/AF-L button to focus does the camera set exposure at this time or does it set exposure when I depress the shutter button?

 

[KmH]

Set to AF-On all the back button does is activate AF.
The button no longer functions as AE-L/AF-L.