Hard starting

My mazda 2 problem is difficult to start the engine.. Ok,every morning i can start the engine as normal. No long crank.. when the engine hot after driving for a long journey/time,i stopped the engine for a stopby or shopping,after 15minute + i want to start the engine,its takes long crank to start and its takes more than 5 second to start the engine. but when the engine stil hot after driving i stop the car less than 5minutes then i start back,its no problem. the engine can start faster... so what the problem??