The first one sounds just fine ("eight" is spelled wrong though), but the second one does not. When you use "sharp," you always say actual time - one o'clock, four forty-five, etc. You could say something like, "half past five, on the dot," and it would sound okay. But, "half past five, sharp," just doesn't have the right flow. Most of the time, people won't perceive it as being rude, unless you are being rude in general before you say that.

Another good example would be: Be there at 5:00 sharp! By adding the word "shap" you are stressing the need to be punctual as if there will be some negative consequence if the person is late (like he'll miss the bus).

It's fine. It means "exactly". Check your spelling. It should be "eiGHt."