Sounds like a fuel pressure leak down problem. It could be the fuel pressure regulator, the fuel pump or check valve. If the pressure leaks down after the warm egine is stopped, the fuel in the injector manifold vaporizes and you get vapor lock. Vaporized fuel cannot atomize and won't burn. So, you continue to crank and crank the engine until the pump eventually pumps fresh fuel at the correct pressure to the injectors and the engine starts. Or, you leave it sit overnight, the manifold cools and the fuel condenses back into a liquid and it will start. Check your fuel pressure. It should be about 44psi running. Check it after you shut the engine off. It should hold at least 30 psi. If it leaks down in a short time, that's your problem.