Yeah but was it already rebuild today? Stick a TO_CHAR around the last_ddl_time

select object_name, object_type, to_char(last_ddl_time, 'DD/MM/YYYY HH24:MI:SS')
from user_objects where object_name= 'TEST_INDEX';

TEST_INDEX,INDEX,06/06/2003 17:17:00

alter index TEST_INDEX rebuild;

select object_name, object_type, to_char(last_ddl_time, 'DD/MM/YYYY HH24:MI:SS')
from user_objects where object_name= 'TEST_INDEX';

TEST_INDEX,INDEX,30/07/2003 17:18:18