Difference between two dates in oracle sql:(Hours HOURS MINUTES SECS)
select request_time, end_time, floor(((end_time-request_time)*24*60*60)/3600) || ' HOURS ' || floor((((end_time-request_time)*24*60*60) - floor(((end_time-request_time)*24*60*60)/3600)*3600)/60) || ' MINUTES ' || round((((end_time-request_time)*24*60*60) - floor(((end_time-request_time)*24*60*60)/3600)*3600 - (floor((((end_time-request_time)*24*60*60) - floor(((end_time-request_time)*24*60*60)/3600)*3600)/60)*60) )) || ' SECS ' time_difference from SINGLE_TABLE_MIGRATION;

change date format display in oracle:
alter session set nls_date_format='DD-MON-RR HH:MI:SS';