I have been asked this question many times in past.
The answer is simple but requires work and analytic reports
The answer is: "when you are ready" and crowd has giving you the signal". These are the steps .
What is the signal?
When you know you can receive at least 30% of the funding goal within two weeks and less after your campaign launch.
1- You need to validate "your idea and concept". By ASKING the question using your CrowdFunding Landing Page ( i.e www.sharkestopper.com) or use a portal such as www.CrowdFundingSoftLaunch.com.
You need to create an inbound marketing plan and get traffic to your portal.
These portals have analytics, call for action and email catching databases , which you can ask your question , find the interest and answer possible questions.
Analytic reports and number of email addresses you collect will be a good indicator or signal.
2- You need to validate your "crowd" , its size and see can you generate enough interest from the crowd ( i.e 100 people) and leverage on their crowd ( I.e 10,000 or more.
To do this and learn the concept, you can use our current program Click here: http://thndr.it/1o0nl3u.
As of today we have 8/100 people and social rich is around 180,000. Campaign one day old and we have 17 days to go .
There are many other techniques success Affinity marketing that allow you to contact Micro angels and habitual CrowdFunding buyers in your vertical of interest .
If you are interested to know more , Just Contactus@CrowdfundingPlanning.com