Calculate timestamp differences between different objects, similar to excel

[#1]

It would be awesome if we could calculate the time difference between 2+ objects in a project. For example in my report I have the "converted issue entry date" and the "project actual start date", because these are two different object types and the issue likely sat idle for some time in the queue before a PM converted it to a project, I want to be able to see what that idle time was by calculating the difference between the project actual start date minus the converted issue entry date.