Problem in Time

Hi..

I got an issue in getting the total time.
I have this code to get the sum of total time:

Code:

$result = mysql_query("INSERT INTO payroll.casual_hours(EMP_NO, Hours) SELECT EMP_NO, sec_to_time(SUM(time_to_sec(Rendered))) FROM payroll.casual_att WHERE DATE_FORMAT(LOGOUT, '%W') IN ('Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday') GROUP BY EMP_NO") or die(mysql_error()); 

Rendered:
09:00:00
09:00:00
09:00:00
08:00:00
08:00:00
07:48:00
and the result of this is 50:48
but I need result is 50:80
the minutes is divided to 60
Is there any way to get the 50:80 result.

Thank you so much..