I phoned DIAC the same question about my AUS work experience before I lodged.
The answer is I HAVE TO meet at least EXCAT one year experience here in Australia at the same day when I lodge my 175 application. It cause me apply on May even I was ready around Mar. So same logic, it should apply to your specific work experience as well.
Why you say system would be shutdown on 27th?Is this ture? May I suggest you check with DIAC regarding the close day even though I dont think it will be happened.Roamer, perhaps!