Formula - based on various cells (not so easy)

Dears good evening
I come to ask for help, for a formula that I need to elaborate.
Enclosed, ou will find an example of the datas that I have in my archive, where I need to calculate the quantity of days between two days.

Always consider the date in column D less the date in column E, but only if number is the same in column J.

Example
Considering Number CRSU9217122
Row 1, because E is blank, nothing will appear, we will leave it blank.
Row 3, we need to consider D5 - E3 (because is the same number in column J)
Row 5, we need to consider D7 - E5

In this example we have only two different numbers in column J, but it can happen that I will have 3, 4 up to 10 different numbers.
In resume, what I need is to find a way to calculate the quantity of days between two dates, if number in column J is the same

Maybe I will need to use VBA, I am a bit confused.
Hope someone will be able to help me.

In case of any doubt, do not hesitate to leave a message.
In advance Thank you !

Dear KjBox,

Thanks for your answer but unfortunately, I would say that it is only part of the answer that I am looking for.
Because I also need to get the count for the other number in Column J.

Thinking also, That the excel file uploaded is only a little part of the complete file.
I will have a lot of different number in column J and for all these numbers I do need to calculate.

I tought to do the same that you offer me but unfortunately it is not enough, for the reasons above.

Maybe I will have to use VBA for this formula...I don't know ??!!

Hope you will try to help me agin.
In advance regards

KjBox good morning.
Sorry I was out yesterday with no access to my computer.

See enclosed sample of the file with result and a comment in ( )

Thanks in advance.
Regards