Your very common sentiment is so logically flawed.  I can't understand how some people can only think in linear terms.  You have exactly two points to draw from... the Model S and the Model X.  You ignore any capacity for a company to learn or improve, and you ignore the very real fact that the Model 3 is a much simpler device to manufacture.  You simply draw a mental line and extrapolate that to the new product.  There's not enough data to say they will be on time, but there's certainly not enough to say they won't.  ALL indications thus far point to them being on schedule.  Why in the world would they order millions of dollars of inventory for their suppliers if they don't expect to actually build the car?