While the solstice (and shortest nights) was almost a week ago week, the latest sunsets occur now. Why is this? Short answer: celestial mechanics. As for why the Sun doesn't have its extreme rise/set dates on the day of the solstice, it all has to do with solar noon, the point in time wherein the Sun reaches its highest point in the sky, which is the basis for the timing of the solstice. Problem: the Sun doesn't always reach its highest point in the sky as seen from Earth at noon. In addition, at the time of the solstice, the lay is actually longer than 24 hours. Result: solar noon doesn't always sync up with measured noon, hence why extreme sunrises and sets do not occur on the Solstices.