There is a thread on the kickstarter campus (a place for creators to ask questions) titled How long did you spend building your project page before you launched?
with some very interesting answers.
Some people say it only took them an hour or two. Other people talk about it in terms of weeks or months. I think there was even mention of a year or more.
What's really neat about this is that you can click on the user's name and follow the bouncy dot to see how many campaigns they have and how successful (or not) each one was. It looks like everyone who claims to have spent less than a week has no successful campaigns. Over a month to prepare seems to have 100% success rate. And a bunch in between.
For those of you who have had a campaign, how long did you take to get ready? How long before you came to kickstarter/ other crowdfunding sites? How long to build your page and make your video?