There are dozens of flight tracking sites out there that can tell you if your flight is on time (or, rather, how late it is). King of them all is fboweb. They get their flight data directly from air traffic control so their information is more current and accurate than even the airlines can provide. Plus, their site includes a ton of features such as the opportunity to listen to live feeds from air traffic control and recent past flights your aircraft has taken. The coolest of all: Your flight’s data syncs up Google Earth, letting you look at a 3D rendering of exactly where on the planet your aircraft is.