The process does change a bit each year, so you should consult the central immersion office. While not mandatory, I believe the open houses are invaluable and they are occurring now. If you are lucky enough to get a spot, it's hard to make up your mind if you actually want it if you haven't been there to get a feel for the school. Another consideration for you should be whether you'll need bussing. Not all school provide this, and depending on where you live the bus ride can be over an hour each way (by car it's 15 min for my kiddo, but one of the magnet busses goes to 5 schools.)