date difference between two columns on two different rows.

Anonymous ,

a new column =

datediff([end date], maxx(filter(Table, [Index] = earlier([Index]) +1 ) , [Start Date]) , day)

or

a new column =

networkdays([end date], maxx(filter(Table, [Index] = earlier([Index]) +1 ) , [Start Date]) , 1)

https://amitchandak.medium.com/power-bi-dax-function-networkdays-5c8e4aca38c

Power BI DAX- Earlier, I should have known Earlier: https://youtu.be/CVW6YwvHHi8