Just did the math:
You would have exactly a 0.000000000082930% chance of hitting a block over a 1 year period running at 99.999% efficiency 24/7 (assuming difficulty remains static)
*And yeah, that's fraction of a single percent!
:-P
What would the math be with 17th?
With 17TH/s you would expect to find a block in about 139 days with the current network difficulty.