Time trails aren't quite what they are. They're time trials like levels, but they are time trials that remix the levels with new enemies/traps/obstacles/patterns. They're also the most challenging content in the game, which as a whole is actually easier than Origins. So the Vita version missing out on the most challenging content is a shame.
There must be a possibility of getting a future DLC for the missing content, right? Here's hoping for an official announcement regarding a patch/DLC from UBIsoft soon.
EDIT: Top of the page for the first time! BUY Velocity Ultra. Worth every penny.