Sorry, I can't reproduce - my tests all come back with "consistent" timestamps, namely, if operations finish within one ms, then the timestamps align, otherwise they do not.
SQL> create table t(seq int, n number, d timestamp default systimestamp);
Table created.
SQL>
SQL> set serverout on
SQL> declare
2 looper number := 10;
3 f int;
4 ts1 timestamp;
5 ts2 timestamp;
6 begin
7 for x in 1 .. 10 loop
8 insert into t (seq,n) values (x,1);
9 ts1 := systimestamp;
10 commit write batch nowait;
11
12 -- burn some time
13 for i in 1 .. looper loop
14 f := i;
15 end loop;
16
17 insert into t (seq,n) values (x,2);
18 commit write batch nowait;
19 ts2 := systimestamp;
20 looper := looper * 6;
21
22 dbms_output.put_line(x||' '||ts1||' '||ts2);
23
24 end loop;
25 end;
26 /
1 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
2 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
3 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
4 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
5 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
6 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.160000 AM
7 10-APR-17 11.39.18.160000 AM 10-APR-17 11.39.18.175000 AM
8 10-APR-17 11.39.18.175000 AM 10-APR-17 11.39.18.408000 AM
9 10-APR-17 11.39.18.408000 AM 10-APR-17 11.39.19.886000 AM
10 10-APR-17 11.39.19.886000 AM 10-APR-17 11.39.28.857000 AM
PL/SQL procedure successfully completed.
SQL>
SQL> select t1.seq, t1.d, t2.d
2 from t t1, t t2
3 where t1.seq = t2.seq
4 and t1.n = 1 and t2.n = 2
5 order by 1;
SEQ D D
---------- --------------------------------------------------------------------------- --------------------------------
1 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
2 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
3 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
4 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
5 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.144000 AM
6 10-APR-17 11.39.18.144000 AM 10-APR-17 11.39.18.160000 AM
7 10-APR-17 11.39.18.160000 AM 10-APR-17 11.39.18.175000 AM
8 10-APR-17 11.39.18.175000 AM 10-APR-17 11.39.18.408000 AM
9 10-APR-17 11.39.18.408000 AM 10-APR-17 11.39.19.886000 AM
10 10-APR-17 11.39.19.886000 AM 10-APR-17 11.39.28.857000 AM
10 rows selected.
Can you give us an example ?