Total Time difference sum not working

TaroGulati , Try creating a measure using

DAX
Time Difference =
VAR TotalSeconds = DATEDIFF(MIN('Table'[Start Date]), MAX('Table'[End Date]), SECOND)
VAR Result_hour = INT(TotalSeconds / 3600)
VAR Result_minutes = INT(MOD(TotalSeconds, 3600) / 60)
VAR Result_second_final = MOD(TotalSeconds, 60)
RETURN FORMAT(Result_hour, "00") & ":" & FORMAT(Result_minutes, "00") & ":" & FORMAT(Result_second_final, "00")

Hi TaroGulati ,

Update your DAX measure to look like this:

Time Difference = 
VAR TotalSeconds = 
    SUMX(
        'Table', 
        DATEDIFF('Table'[Start Date], 'Table'[End Date], SECOND)
    )
VAR TotalHours = INT(TotalSeconds / 3600)
VAR TotalMinutes = INT(MOD(TotalSeconds, 3600) / 60)
VAR TotalSecondsFinal = MOD(TotalSeconds, 60)
RETURN 
    FORMAT(TotalHours, "00") & ":" & FORMAT(TotalMinutes, "00") & ":" & FORMAT(TotalSecondsFinal, "00")

Your output will look like this: