I didn't see anyone else reply to this, so apologies if you already got a response.
You cannot unlock 20% of your memories until after the activity check for your first month here. So you'll post your July activity check and once it's approved you can put in for memories. You'll also be able to get your 2 items a month at that time.
If you comment on the reference information (memory table check, AU, job, alumni, etc) then you get 1 memory per comment made. These comments can be redeemed before the activity check since they are not dependent upon your activity. However, they can only be done once while you're in the game.
If you have anymore questions let us know. -Lauren