To calculate the number of days between two dates for each query record

Just wondering if I can get some help in the following:

I have the requirement to calculate the number of days between two dates. The request is to run this calculation for each record from the query.

I started to investigate how to do this using Virtual Characteristics and Virtual Key Figures. I have created the cube in which I have two Characteristic dates as sources (0CLEAR_DATE and 0NETDUEDATE) and the target as a Key Figure (0NUMDAY), with the aim to use the 0NUMDAY as Virtual Key Figure.

My question is which BAdi to use for this and how to implement this successfully? Thank you.