Google says that this feature works for almost any location. "Whether you're looking to find the best time for a morning jog or trying to plan that perfect moment for a wedding proposal, knowing exactly when the sun rises or sets can always be helpful. (...) Unlike the weather, sunrises and sunsets are quite predictable, and as a result, we don't use a data source. Instead, we calculate sunrise and sunset times based on latitude, longitude and the current time. This calculation has been of interest to astronomers and mathematicians for millennia, so they've had time to get it just right. And for most locations, it's accurate to within a single minute."
You can also type [sunset] or [sunrise] and Google should show accurate information for your location. Google has similar OneBoxes for weather and time.
