Sandi, I'm pleased you and your DH enjoyed the article. I was surprised when I gave a presentation last spring to the Master Gardeners in the area that a lot of the men were VERY interested in making a sphere.
Tee, I made a few in the basement last winter, my "new" workshop.
It's unheated but I used a small space heater to keep the area at least 60 degrees while I was working. Another trick one of the "crete artists" suggested was to use a heat lamp and drape a large tarp over the sphere while it was curing.