It took me 3 or 4 days to get selected as well which was why I called them to ask the same question.
All she knew was the system was 100% automated and that it checks all the profiles 'at some point', not every day. And when it does check profiles, it is not checking every single profile every single day. To me that sounds like it's checking batches of EE profiles at a time?
The main advice though was if you meet the criteria on their website and there are still places left, you will get an invite so be patient. All of the other stuff about NOC codes, age, etc being factors are just people on this forum spouting nonsense.
Speculating a little, there may have been no PTs sent out for a few days to allow them to manage the applications and paperwork at their end. I'm sure they don't want 2,700 applications dropping into their office at the same time so maybe they're just spreading the load?