DATE_DIFF() Between 2 Custom Attributes

I recently tried to create a custom attribute that used the DATE_DIFF() function to get the time between 2 custom timestamp attributes. 

I have been advised by a Zendesk Support agent that it is not currently possible to create a custom DATE_DIFF() attribute/ metric that will get the time between 2 custom timestamp attributes.

I feel that this is a huge oversight as in reporting I need to compare 2 events that are not native Zendesk attributes, i.e. the time between a group assignment and the time a checkbox was filled. This feature was available in Insights can this please be made available in Explore