At 99designs, quality and trust within our design community are of the utmost importance. As a way to motivate Entry Level designers to improve their skill sets, we have set limits on contest participation.
Entry Level designers have been reviewed based on our quality standards. Time is not a factor.
Although we keep in mind things like wins and repeat clients, this is ultimately based on designers' overall design quality and how well you adhere to 99designs’ site policies including concept originality, code of conduct and stock image/clip art.
The current limit for Entry Level designers is 15 contests in any 28 day period. Each of these 15 contests are on rolling counter, meaning they don't all "reset" at once. It may help to think in terms of 15 open "slots". 28 days after you have used one of those slots it will become available again. This method is used to avoid a rush at the end of a calendar month.
We hope this will encourage designers to spend more time and thought on each of their designs, work more comprehensively with clients and take more pride in the work they submit.