time_zone

tz

SQL> select sessiontimezone from dual;

SESSIONTIMEZONE
---------------------------------------------------------------------------
+04:00

1 row selected.

SQL> declare
  2      tstart      TIMESTAMP;
  3      tstop       TIMESTAMP;
  4      tdelta      INTERVAL DAY TO SECOND;
  5      tdelta2     INTERVAL DAY TO SECOND;
  6  begin
  7      tstart := systimestamp;
  8      dbms_output.put_line('Start: ' || to_char(systimestamp));
  9      dbms_output.put_line('Sleeping');
 10      dbms_lock.sleep(1.5);
 11      tstop := systimestamp;
 12
 13      dbms_output.put_line('using current systimestamp: ' ||to_char(systimestamp - tstart));
 14      dbms_output.put_line('using two variables: ' ||to_char(tstop - tstart));
 15  end;
 16  /
Start: 2014-06-11 23:56:50.168000000 +04:00
Sleeping
using current systimestamp: +000000000 00:00:01.500000000
using two variables: +000000000 00:00:01.500000000

PL/SQL procedure successfully completed.

SQL> alter session set time_zone='+03:00'
  2  /

Session altered.

SQL> declare
  2      tstart      TIMESTAMP;
  3      tstop       TIMESTAMP;
  4      tdelta      INTERVAL DAY TO SECOND;
  5      tdelta2     INTERVAL DAY TO SECOND;
  6  begin
  7      tstart := systimestamp;
  8      dbms_output.put_line('Start: ' || to_char(systimestamp));
  9      dbms_output.put_line('Sleeping');
 10      dbms_lock.sleep(1.5);
 11      tstop := systimestamp;
 12
 13      dbms_output.put_line('using current systimestamp: ' ||to_char(systimestamp - tstart));
 14      dbms_output.put_line('using two variables: ' ||to_char(tstop - tstart));
 15  end;
 16  /
Start: 2014-06-11 23:56:51.671000000 +04:00
Sleeping
using current systimestamp: -000000000 00:59:58.500000000
using two variables: +000000000 00:00:01.500000000

PL/SQL procedure successfully completed.