Welcome to Flyertalk
MatFlyer 
You have posted in the right forum, the best of FT of course
What you said is right : the front Y cabin (in whole or in part) can be pre-assigned only for Elites/Elites+ pax, and they are available to anyone when OLCI opens, i.e 30 hrs before departure. I don't think there is any way for you to have them before.
And to tell you usually how much of those seats are indeed available at OLCI, I'm afraid it's absolutely impossible to give you an answer, as this can vary considerably across flights, days, seasons, etc. The period of your flight should be during or close to the soccer World Cup, right ? If the case, expect some very very full flights. So, at that stage, my advice is that you must secure a good seat where you can pre-select one (otherwise you'll get stuck in a middle seat), and see at OLCI what you can do as soon as they open it.