turtle eggs hatching

Question
Last night we were walking out in the flower garden and noticed a turtle laying eggs in the pea gravel along the walkway.  She had a fairly flat dark green shell with no real markings on it and it looked like she had yellow lines along her neck.  She used her back legs to bury the eggs and later when we went to check on it she was gone and the area just has a little indentation but is covered with the gravel again.  We got a short clip of her burying the eggs and would like to know when to start watching for them to hatch and possibly catch it on film also to share in my science class next Fall.  We are in Iowa.  Any idea how long the eggs may take to hatch?  

Thanks!

Answer
Could be a Map or Painted Turtle. Their eggs will hatch in an average of 2-3 months, with a possible range of about 20-320 days. The variability makes it tough to plan to film or watch the hatching.

Many species will also hatch, but stay in the nest until most of the eggs are hatched, then they all come out at the same time to improve their safety.

Try http://www.austinsturtlepage.com for more info on these species.