Array formula looking at a specific value in Column A skip a row and return a value

Good Evening,

I am hoping to find a way to write a formula that looks at a specific value in column A (in my sample "X") and then skips a row and looks at the series in Column C and returns a value of the difference of the last two entries in the series.
Then looks for the next value of "X" in column A and repeats the calculation until there are no more values of "X" in Column A

Re: Array formula looking at a specific value in Column A skip a row and return a val

I've tried this as a formula but I get a #NUM error.

=DATEDIF(LARGE(C5:C28,1),LARGE(C5:C28,21),"D")

Re: Array formula looking at a specific value in Column A skip a row and return a val

sorry, I meant this formula

=DATEDIF(LARGE(C5:C28,1),LARGE(C5:C28,2),"D")

Re: Array formula looking at a specific value in Column A skip a row and return a val

I've also tried the below but also get the #num error

=NETWORKDAYS((INDEX(LARGE(C5:C28,1),1)),(INDEX(LARGE(C5:C28,2),2)))