Every time I have seen the 'clear prop' call being said, the prop starts turning about 3 nanoseconds after the call
Yep, either that or the person is almost embarressed to be shouting, so just sort of mumbles clear prop out of the window so theres no way anyone could hear.
It should be a clear shout with the emphasis on the "PROP", pause, double check the area is clear and then start cranking.
The other problem is where you've failed to start 1st time, perhaps leave it 30 secs or so and then start cranking again without looking out or recalling. By this time, someone has usually seen you've had trouble starting and is heading over to add their 2p, making the situation slightly more dangerous.