Seconds difference between 2 dates

hi, Anonymous

DATEDIFF Function is dax function and in the query editor it needs M language, 

In query editor you can do these achieve your requirement

Step2:

Add a custom column that two datetime column are directly subtracted

Step2:

Select the result column then click Transform->date&time column->Duration->Total seconds

Result:

And the modeling process

you could create a calculate column by DATEDIFF Function

calculate column = DATEDIFF(Table1[Datetime1],Table1[datetime2],SECOND)

Best Regards,

Lin