For this achievement, Buford asks you to complete five races:
1) Complete level 1-1 in less than 3:00
2) Complete level 2-2 in less than 5:20
3) Complete level 3-2 in less than 3:40
4) Complete level 3-4 in less than 6:00
5) Complete level 4-1 in less than 6:20
I was able to beat all 5 races on the first try, I don't think any of them were very challlenging as long as you are not spending time trying to look for collectibles.