What sort of container is it in? In a flat dish it might be aday or two. In a tall narrow class it could take a couple weeks. The rate of evaporation depends on how much of the liquid is exposed to the air. Temperature is also important, as is air movement.
The carbonated water will evaporate after about 14 days (uncovered) however, the sugar will stay int the cup. Its actually pretty cool, but disgusting. I actually stopped drinking orange soda after i tried this "experiment"