Your temperature range is a little low for the 60 day hatch time. I think mine went about 70 days (without actually going too look it up) at a slightly warmer temperature than what you are using.

Here are two sites that gives a longer number of days...
http://www.peteducation.com/article.cfm?cls=17&cat=1796&articleid=3128
http://www.angelfire.com/wizard/coicwebdesign/page1.html