Calculate date difference for a specific column value+ exclude values

Ok thank you for your reply, I manage to get the measure I expected from that topic. 

So the first calculated column gives me the date of the last production for each product group row : 

Date_Previous_Campaign = 
MAXX (
    TOPN (
        1;
        FILTER (
            TABLE;
           TABLE[Product Group] = EARLIER ( TABLE[Product Group] )
                && TABLE[DATE] < EARLIER ( TABLE[DATE] )
        );
       TABLE[DATE]; DESC
    );
    TABLE[DATE]
)

Then I create a second calculated column to calculate the duration between two production orders : 

Days since last campaign = DATEDIFF(TABLE[Date_Previous_Campaign];TABLE[DATE];DAY)

Then eventually my measure of average, excluding values under 3 days to really focus on campaign : 

Average Duration = CALCULATE(AVERAGE(TABLE[Days since last campaign]);TABLE[Days since last campaign]>3)

Thanks for your answer, I got the result I expected. However it might not be the most optimized solution. 

Have a good day !