What is exactly LAST_DDL_TIME?

What is exactly LAST_DDL_TIME? Is it the START time for the DDL event, or the END time indicating that the DDL event was successfully completed? Can the LAST_DDL_TIME be used as a trigger to launch a process that requires the DDL event to have been concluded?

pretty sure its the end time, but test it out - rebuild an index on a test database, see when it starts and finish and see what date goes in

Thank You. Your answer helped me. LAST_DDL_TIME is sthe time when DDL event is completed.