I need time based format too. Amazon do mention time based leaderboards here: "Leaderboards are ranking of a player's score against other players of the same game, such as displaying the highest score or the shortest lap time." -
https://developer.amazon.com/public/apis/engage/gamecircle/docs/get-set-up-for-gamecircle However, when you try to create one in the dev portal, the best I can manage is to just use 'ms' (as in milliseconds) for score units. Not ideal, but hopefully Amazon won't reject an app for that?
I tried to use "Hundredths of second" but there is not enough room in the text box for the units. So I used "0.01 seconds" :/ It's kind of ugly but in the future when they add different presentations of the score I might be able to change that and have the right scores.