This achievement is for getting a silver medal on any 5 challenges. Its not to difficult, I got silver on 5 without much effort. But what worked for me may not work for others, so I will list the times needed to silver medal the first ten challenges. You need to beat a certain time, 2 of which you need to last for a certain amount of time.
1. The Combat Trial: 00:45
2. Kamino Drill Grounds Trial: Last 2:00
3. Deadly Path Trial: 00:43
4. Deflection Trial: Last 2:00
5. Retrieval Trial: 1:10
6. Domination Trial: 2:00
7. Terror Trial: 1:40
8. The Cloning Spire Trial: 00:15
9. Scout Trooper Trial: 1:30
10. Gauntlet Trial: 2:30
If anything needs to be added or adjusted please let me know, hope this helps some.