There's no such thing as early warning for an earthquake. They can't be predicted.
What they can do is make predictions as to what faults are "due" using the history of quakes on that fault, the amount and speed of movement in the plates that cause the faulting, any deformation surrounding the fault, the type of crust in which the fault occurs, and a whole host of other factors and calculate roughly how much stress has accumulated in the fault since it was last released versus how much stress the fault can likely withstand before it goes off.
That's how they can determine a certain fault has a certain percent chance of a certain size quake within a range of years. But there are too many known and unknown variables, that's as close as they can get at this point.
Sorry to burst your bubble, even a few minutes' warning could save a lot of lives. Maybe some day! With the number of people in the US and worldwide living in dangerous fault zones, the research should be a high priority.
Thanks for doing my homework for me. I've got to go read up on that and how it works. If they can predict quakes now even minutes in advance that's huge. Or if they're basing a warning system on the amount of time it takes the waves to travel from the epicenter to populated areas, it's still worth doing. Thanks!
