As a contest holder, how much time do I have to appoint a winner?

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You have 3 weeks to appoint the winning design of the contest. If you haven’t appointed a winner at the end of 3 weeks, the designer with the highest rating for his/her design will be set as the winner. If none of the designs received ratings, then has the rights to randomly select the top 4 winners based on the rating. However if none of the designer is given a rating, then will randomly choose 4 winners.