Could be a leaking injector (mains or cold start) or bad FPR. A fuel pressure leakdown test and/or pulling the fuel rail and injectors would help confirm that.

Within the first hour there might not be much fuel leaked, but the longer it sits the more fuel will puddle up in the intake until all the pressure in the fuel system has dissipated. This puddle of extra fuel could cause an artificially rich condition for the first few minutes of starting.

Wait long enough and eventually the engine is cold enough to use the extra fuel, some of which might have worked its way past the rings (into the oil).

Pull the plugs immediately after a failed start and see if they are wet, fouled with gas.