I recently came across an interesting study in MarketingProfs “Get to the Point” newsletter. They wanted to see if people were more likely to click on a link labeled “Take a brief survey” or “Take a 5-minute survey”, when sending an email survey. The five minute version resulted in 8% increase in clicks, 9% increase in the number of people that started the survey after being taken to the landing page and 11% increase in the number of people that actually completed the survey.
Take away point: Be as specific as possible when asking people to give up their time for your cause. It might not be the magic solution to getting more people to fill out your survey, but as the results indicate it is a step in the right direction.