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A Contest has 3 phases, Entry, Voting, and Complete. You can set the dates when the Entry begins, when the Voting begins (which means the Entry Ends), and when the contest is Complete. This is the most fair way to run a contest because this means each entry will have the same amount of vote time. Optionally you can allow Entries while the Voting is occurring, but this is not the most fair way to run a contest.
Click this, and use this tool to build and keep track of things you have to do.