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@unprovoked I've submitted my post in 15 seconds after 06:00 PM, will my submission be counted?

Yes, 15 seconds is fine. It is open while the contest says "OPEN". It is closed a bit later than 6 PM to allow for errors due to timezones etc. Once the contest changes status to "CLOSED" then it is too late. I try to be as flexible as possible though, I understand that Steemit is an international community.