@Dr Abegod,
The records say 1s, 2s, 3s which stands for seconds. You could have them as 20 points, 15 points and 10 points as you described in the challenge description.
To do that:
In the challenge edit page, use "points" for unit and "Highest" for Records/Times Order. Then edit records and give players 20points, 15points 10points etc...