The development schedule for a new U.S.-Israeli missile interceptor system is overly ambitious, and defense authorities likely will have to implement a backup plan if countries like Iran acquire a nuclear-tipped missile before the end of the next decade, according to defense experts. Advanced sensor and propulsion capabilities envisioned for the Arrow-3 interceptor likely will take significantly longer to develop than the five or six years estimated by Boeing Co., particularly given the program’s funding level, the experts said. “Look at any system that is developed — it takes 10 years from concept to deployment and there’s not much [funding]...