Time trial is a Re-Volt offline game play mode. It's all about racing alone/against Ghost car in no pickup mode in order to get the fastest time. Ghost car requires a special Re-Volt version (early demos such as DEV, or additional memory patchers such as Wolf R4 and Phoenix R3).
Beating all same difficulty track challenge times, unlocks reversed (R), mirrored (M) and mirrored reversed (RM) track modes for same tracks.