Market Ultra Shortcut

Setup

Use boosted wall climbing to get above the map on the first optional arena. It's likely you'll need multiple boosts because of the weird geometry. To avoid the game's nosedive mechanic, wait for your first boost to end before using the second one. 

During the skip

After landing out of bounds, quickly turn right to avoid triggering the out of bounds timer, from there drive straight forward until the end of the platform. 

Landing

Boosting off of the corner can give you enough height and speed to corner cut back in bounds and save just a little more time.