Fuel pressure is bleeding down over time. Usually that's caused by one of the injectors leaking but it can also be caused by a leaking check valve in the pump or a leaking pressure regulator. None of those are particularly serious. If I'm right, it will start faster if you turn the ignition switch to "run", then wait for two seconds before cranking the engine, or if you cycle the switch to "run", turn it back off, then turn it back on and crank the engine.