datediff in HH:MM format

Duration HH:MM:SS = 
// We start with a duration in number of seconds
VAR Duration = DATEDIFF( 'Table'[StartDate], 'Table'[EndDate], SECOND )
// There are 3,600 seconds in an hour
VAR Hours =
    INT ( Duration / 3600)
// There are 60 seconds in a minute
VAR Minutes =
    INT ( MOD( Duration - ( Hours * 3600 ),3600 ) / 60)
// Remaining seconds are the remainder of the seconds divided by 60 after subtracting out the hours 
VAR Seconds =
    ROUNDUP(MOD ( MOD( Duration - ( Hours * 3600 ),3600 ), 60 ),0) // We round up here to get a whole number
// These intermediate variables ensure that we have leading zero's concatenated onto single digits
// Hours with leading zeros
VAR H =
    IF ( LEN ( Hours ) = 1, 
        CONCATENATE ( "0", Hours ),
        CONCATENATE ( "", Hours )
      )
// Minutes with leading zeros
VAR M =
    IF (
        LEN ( Minutes ) = 1,
        CONCATENATE ( "0", Minutes ),
        CONCATENATE ( "", Minutes )
    )
// Seconds with leading zeros
VAR S =
    IF (
        LEN ( Seconds ) = 1,
        CONCATENATE ( "0", Seconds ),
        CONCATENATE ( "", Seconds )
    )
// Now return hours, minutes and seconds with leading zeros in the proper format "hh:mm:ss"
RETURN
    CONCATENATE (
        H,
        CONCATENATE ( ":", CONCATENATE ( M, CONCATENATE ( ":", S ) ) )
    )

This is code from:

https://community.powerbi.com/t5/Community-Blog/Aggregating-Duration-Time/ba-p/22486

Best

Darek