The field includes 7 days, it could be any of them, within 2 minutes of the time chosen in those days, there are 10080 minutes in a week, divided by 2 is 1/5040 chance per post.why seconds, when it is to the nearest minute?
the day you posted doesn't matter either - last week a winner could have posted at 18:10 on monday, or 18:10 on friday, or....
so i think the odds are 4/1440 all multiplied by the number of unique guesses you have - but that doesn't take into account the fact that a spot-on guess would win instead of a guess 2 mins away.
While my earlier calculation was over-complicated, it's still correct.
60(minutes)x24(hours)x7(days)/2(minutes) = 5040