MATERIALIZED VIEW 12.2

when I run this procedure:

EXEC DBMS_MVIEW.REFRESH('mv_test_view', method => '?');

...it completes after 291 seconds. But looking at the refresh stats:

SELECT * FROM DBA_MVREF_STATS WHERE mv_name = 'mv_test_view' ORDER BY refresh_id DESC;

... it shows only 189 seconds were taken.  Why the difference of ~100 seconds?