You are using wrong format mask for TO_CHAR function (and I copied your wrong format mask in my response ). You should use 'hh24:mi:ss' instead of 'hh:mm:ss'. 'MM' is used to represent month number (01 to 12), while 'MI' is used to represent minutes (00 to 59). So the correct usage is:

select to_char(sysdate+ 2/24 + 35/(24*60), 'hh24:mi:ss') from dual;