When do I harvest buttercup (not butternut) squash?

Answer 1

Buttercup Squash is part of the Turban squash family (hard shells with turban-like shapes) and are a popular variety of winter squash.
http://whatscookingamerica.net/squash.htm

It is time to harvest your winter squash when the “ground spot” changes from white to a cream or gold color... the skin is hard... and the fruit sizes up and then takes on a dull waxy appearance.
Leave the stems on turban and buttercup squash.

Bring in well before the first cold snap. Since most squashes are warm season crops, they are susceptible to low temperature injury at less than 50 degrees. Squashes and pumpkins left out in the garden may become cold-injured and will decay prematurely in storage. Once the weather gets below about 50 degrees for more than a week, or there is an extended period of rain, pumpkins and squash should be brought in for storage.

Cure squashes after harvesting them by holding them at warm, dry temperatures for a few days until any abrasions or cuts from harvesting heal up.
http://www.dhonline.com/articles/2006/09/26/news/home_garden/home01.txt

Good luck! Hope this is helpful.