Difference between two dates in two rows in a matrix

Look into EARLIER and EARLIEST functions.

See if this gives you what you need...   you had your blank on the first line, but my logic moves the 'unkown' to the last line.  To do calcuations, I had to choose some 'date' to end the logic so I put code in there to always use MAX(Date) at the end of the file.  This is neccessary to 'skip' the final Version comparison b/c there's no higher versions to compare it too...  I also want to give a Shout Out to this AWESOME article that helped me understand EARLIER/EARLIST to write this 'first time use' code...  http://tinylizard.com/dax-earlier-function/

If anyone has an easier way, please feel free to jump in!

FOrrest

Calculated Clumns:

End of Version = IF( Table1[Version] = MAX(Table1[Version]),MAX(Table1[Date]), // Figure out what to do when we reach the MAX Version number since there's nothing higher than it to use to calcute a higher date...  I've put in the MAX date, but you will need to descide how you want to handel this???
CALCULATE( MIN (Table1[Date]), // For Non Max Version Numbers Get MIN Date by...
FILTER(ALL(Table1), Table1[Date] > EARLIER(Table1[Date])), // A Row GREATER Than the current Row for Date
FILTER(Table1, Table1[Version] > EARLIER(Table1[Version])), // A Row Greater Than the current Row for Version
FILTER(Table1, Table1[TaskState] = "Success") // That's a SUCCESS
) -1 ) // Go back 1 day & Close the IF Statement

Measures:

Min_Date = MIN (Table1[Date])

Interval = DATEDIFF([Min_Date],AVERAGE(Table1[End of Version]),DAY)

Thanks fhill - that looks like an interesting approach, but I couldn't quite get it to work.  I'll keep a note of it though.

v-yulgu-msft - that does exactly what I want thank you very much for your help.  I only needed to tweak earliest date last version slightly to work with my actual data.

I think a good think for me to investigate next would be having the measure react to any filters that are applied instead of hardcoding it in the measure.

Thank you.