I am not genuinely sure if there is some significance behind it, but having just 28 hours does not seem to be enough, in my opinion. I would appreciate 48 hours, perhaps.
To be clear, this statement and opinion is NOT affected by where my nation ended up; I still feel that even for the top nations, there is so much fluctuation, it's like a leaderboard based on the range of 0-20 WA Endorsements, where a single endorsement can significantly change things.