Turtle eggs hatch between 8 and 10 weeks after they are laid. While breeding and egg-laying habits vary slightly between different species of turtles, most species have roughly the same incubation period.
According to About.com, sea turtles mate in the ocean. Afterwards, the female turtle swims to the shore to lay her eggs. She buries the eggs in the sand and leaves them there to incubate and hatch.
Common box turtles may mate on land or in the water and the female box turtle usually lays her eggs in a nest on top of the sand instead of burying them.