Have similar issues with our 67 2V 289 C code.
Best explanation I've heard: Ethanol-blend fuels are more volatile, and will evaporate rapidly in a hot engine with a vented carburetor float bowl.
And it will take some cranking over to start the hot engine while the float bowl is refilled by the fuel pump. In a cold engine, fuel evaporation doesn't happen as quickly, although sitting a for few days may bring on the same symptoms.
If you try to start the hot engine within a few minutes after shutting down, it likely will fire quickly. With a longer interval, the still-hot engine will start only after the starter motor cranks for a while.