group data in timestamp

SELECT to_char(last_upd_ts,'HH24:MI:SS'), count(*) FROM COMM_MSG_QUEUE WHERE last_upd_ts > TO_DATE('30-May-14 18:29:00', 'DD-Mon-RR HH24:MI:SS') group by to_char(last_upd_ts,'HH24:MI:SS')order by to_char(last_upd_ts,'HH24:MI:SS') asc;