Most growers frown on miracle grow, because it has a tendency to cause burn.
At that size it might take a bit to see the burn (if its bad it might show up quick). I've really only ever experienced it with smaller plants (5 inches or less and only 4-5 nodes), and then I can tell within a day or so at most. If the signs are obvious within a day to a day and a half I figure it is bad enough to worry about. If it takes longer than a couple of days, then I usually ignore it, because the damage is done, but its probably not serious enough to warrant drastic actions.
Like I said, it will probably be different for plants your size. They have the ability to use those nutes a lot faster.