If my memory serves, the daily change isn't constant -- it describes a curve, with the daily change getting smaller as it approaches each end (summer and winter solstice.)
The US Naval Observatory publishes data on sunrise and sunset.
Try this page for more info than you could possibly want <grin>.
If you have a handheld device, you can get an application that will determine various sun/moon data. I use Focalware for my iPod Touch, though it works better on an iPhone with the built in GPS.
Now that you have discovered this fact, you'll find it to be very useful for landscape and architectural photography. For example, my campus has several buildings that face mostly north. I can figure out what sort of light I want on the front, then what week I need to shoot to get that light.