^ Having said all of that, be aware as well that the "scheduled" date is nothing more or less than a "best estimate", at least until such time as construction is well under way. Construction almost never begins until the project has been at least 60% sold, as banks won't advance money prior to that point. Other unanticipated delays may also occur of course, before or during construction.
Your Agreement of Purchase and Sale will contain some small print which basically allows the builder to defer closing, subject to giving you notice within specified time periods. Hopefully you will have read this.
Don't make final arrangements to move out of your existing accommodations until you are quite sure of your move-in date at the new place. (Sorry if it sounds like I am stating the obvious, but some people have learned this the hard way :\ )