|MadSci Network: General Biology|
Since I don't know exactly which species of turtle chose to lay her eggs in your yard, these answers will be very general. If you remember what she looked like, you may be able to get more specific information from the library or from the web sites I've listed at the end of this message.
The length of incubation (or amount of time it takes for eggs to hatch) depends a lot on weather conditions. Temperature, humidity, rainfall, and other factors influence incubation. Generally, land turtle incubation ranges from 45-90 days (I know that's a long time to wait when you want to see baby turtles!).
I suggest you start checking on the nest every couple days starting at the six week point. I wouldn't expect to see any babies until August at the earliest.
As far as protecting the nest, turtle moms usually choose their nest sites carefully. Unless you think the eggs are in danger, just leave them where they are. If you have a dog, don't let him or her get close enough to the nest to dig it up. Raccoons and opossums also like to eat turtle eggs, so that might be a problem as well. Even though it's hard, I would recommend you just let nature run its course, and hope you get a chance to see the babies when they emerge.
You can get more specific information on several web sites:
This site shows pictures of different turtles so you can determine which species came to your yard. Then you can read more about hatching time, habitat, and behavior of all kinds of turtles.
This site is mainly used by people who keep turtles and tortoises as pets. You can learn more about hatching and feeding turtles, and talk to other kids who have been lucky enough to have turtle visitors.
A great site for books on turtles and tortoises. Or visit your library.
Have fun, and don't worry about the hatchlings once they emerge. They know how to find food and a good place to live.
Try the links in the MadSci Library for more information on General Biology.