When you enter the Race Time Trial, you will see some levels, and on all of them, exist a Velo Time, select a level, and then the Velo icon (if you have beaten N. Tropy's Time.)

Unlockable	How to unlock
Beat Android Alley's Velo Time.	Finish the race in less of 3:05.71.
Beat Assembly Lane's Velo Time.	Finish the race in less of 2:32.76.
Beat Barin Ruins's Velo Time.	Finish the race in less of 2:08.71.
Beat Clockwork Wumpa's Velo Time.	Finish the race in less of 2:37.15.
Beat Deep Sea Driving's Velo Time.	Finish the race in less of 2:39.46.
Beat Electron Avenue's Velo Time.	Finish the race in less of 3:55.52.
Beat Hyper Spaceway's Velo Time.	Finish the race in less of 4:29.41.
Beat Inferno Island's Velo Time.	Finish the race in less of 1:38.44.
Beat Jungle Boogie's Velo Time.	Finish the race in less of 1:35.00.
Beat Meteor Gorge's Velo Time.	Finish the race in less of 1:51.94.
Beat Out of Time's Velo Time.	Finish the race in less of 2:35.19.
Beat Thunder Struck's Velo Time.	Finish the race in less of 3:21.05.
Beat Tiny Temple's Velo Time.	Finish the race in less of 2:24.62.