Looks like it's pretty variable by species as to when they hatch:
Green Sea Turtle: At around 45 to 75 days, the eggs hatch during the night, and the hatchlings instinctively head directly into the water. This is the most dangerous time in a turtle's life.
Leatherback: The eggs hatch in about sixty to seventy days.
Loggerheads: 80 days
Olive Ridley: The incubation period is usually between 45–51 days under natural conditions, but may extend to 70 days in poor weather conditions. Eggs incubated at temperatures of 31-32 degrees Celsius will produce only females; eggs incubated at a temperature of 28 degrees or less will produce solely males; and incubation temperatures of 29-30 degrees will produce a mixed sex clutch2. Hatching success can vary by beach and year, due to changing environmental conditions and rates of nest predation.