They normally try to have them up by the third weekend in May; the 16th is just before that weekend, so without some "inside info" it's hard to say, if you're actually going to try the trek on Friday the 16th.
I took a gamble on setting up our Half Dome trip during the following week (just after the third weekend), and figured if they weren't up, we could do the rest of the hike anyway, or do another, perhaps Eagle Peak etc.
Offhand, I'd say you have a good chance, just keep some other option in mind just in case. You can hike as far as the base of the cables, and if they're up, continue, if not, it's still a great hike. They do post a sign at the beginning of the John Muir Trail, but it may not go up immediately when they finish.
Gary
Yosemite Photo Galleries: http://www.pbase.com/roberthouse/yo