Formaula to calculate the downtime monthwise

Hello Friends/Sirs
I am seeking help on an excel sheet as attached herewith, “Data” is source file where all the data is present.
In “Monthwise downtime” sheet I want to calculate the downtime monthwise between two date ie. Under column C & J.
I have calculated the downtime but it is all going into July Month as I considered Start date as reference to calculate the monhwise downtime.
Please can anyone to solve my problem.

Thanks & Regards
Nitin