You can vote unlimited times, and the deadline is every Sunday 9:59am EST / UTC-5 (11:59pm KST / UTC+9). The poll is restarted every Monday around 8:00pm EST / UTC-5 (Tuesday 10:00am KST / UTC+9)
About Ranking System
To determine the score of the weekly ranking songs, the following is taken into account: 1) Votes of listeners (1 to 20 points): the song with the most votes will have 20 points. The song with less votes will have 1 point. Songs are ordered from 1 to 20 according to the number of votes. 2) GAON Chart (1 to 20 points): The songs will have a bonus of 1 to 20 points, if they are in the most recent weekly GAON Chart. 3) Votes of DJ's (1 to 20 points): The DJ's will vote for the songs according to quality criteria, without bias. Score from 1 to 20 will be assigned to each song.
Final Score = 75% x Listeners votes + 15% x GAON chart + 10% x DJ's votes.