I don't think that there is a problem with them putting up a temporary marquee. I do think that it will be a temporary and not the real thing. However, there is nothing wrong with doing it this early because there are a lot of people who visit new york city this time of year and also visit it in the fall. It will get people to realize that this show is coming to NYC.
Besides, I doubt that this is the first Broadway show to have a temporary marquee or a show that will change it later on.
"If you try to shag my husband while I am still alive, I will shove the art of motorcycle maintenance up your rancid little Cu**. That's a good dear"
Tom Stoppard's Rock N Roll