I have a spreadsheet with many rows (1000s) and columns. I am trying to
determine how long it took for a percentage of franchises to open. Lets say
I have:

Column A: Company Name
Column B: Date when product was ready (ie Company A would have the same date
on each row )
Column C: Franchise Name
Column D: Date franchise opened.
Column E: Col D - Col B

If there were a 1000 rows, 500 of which were for company A. I would like to
find the amount of time it took for 50% (the first 50 sites for this example)
of the franchises to open. I am thinking it has to order the dates in column
D, then find the franchise that was 50th and then take column E as the
answer.

I get that it is an array, but get stuck after that.

Ideas.