I personally have no clue. You should really be bothered about the 1000 cap for Mech Engg, rather than the 25K overall cap.
Last year Computer Programmers were the first to fill up, and they say that it got filled sometime in the middle of August. I am not sure if they started opening the applications in August of those who submitted in May, or they accepted applications till August. At that time the cap was 300.
I too am new to this, but I feel you should be ready to submit your application as soon as you get the ECA in the end of May. I doubt Mech Engg would have 1000 applicants by the end of May. Fingers crossed.
