a controlled hover that you can enter and exit at will, at least in my book 30 seconds+, but you need a plane capable of sustained hover. 5-10 seconds and you aren't controlling the plane in the hover, it just happens to stay there because of inertia. keep it there 30 seconds and that would be hovering.

I can put my mini IFO vertical, hang it on the prop, but i don't consider that a hover. No rudder on it and it starts to get away from in usually 10-15 seconds max.