Here's my thoughts on the 18th.
Since NBC/Universal parent company owns both Univ. Studios and the Today Show, it's a safe bet that the Today Show will be covering the GO live that morning, rught up until they go off the air, (which is some areas is 11am Eastern Time). So count on them roping off large sections of WWoHP to guests all morning.
My bet would be, if they are honoring the Breakfast ressies at Three Broomsticks, that parts of Hogsmeade would be accessible.
Now if I was the PR person in charge, I'd set the ribbon cutting ceremony up right in front of Hogwarts Castle, the iconic symbol, known to HP fans worldwide. I'd have the frog choir and dancing Beauxbatons girls right there in their area performing for the cameras. I'd have the media lined up from the JP bridge to DC's exit area. I'd have the actors and VIPs in front of the winged hog statues and that cool rock formation leading into FotH and at Hagrid's Hut. Then after all the speeches are made, the balloons released and JKR cutting the ribbon, I'd let all the VIPs into Hogwarts for their first rides of FJ.
And then, around one, when the media and VIPs are done, I'd drop the ropes at the end of Hogsmeade and let the masses in.
And then, after about an hour of heavy cycling, when the lines have reached the 5+ hour wait time.... the ride will breakdown.
So, to answer your question..... Maybe.

Sorry, if it seems like I'm making fun, I'm not, really, I just don't see that many people getting to ride FJ on the 18th, so I'll keep my fingers crossed that you get a soft/preview beforehand.