Undermine Skyrocketing: Bronze

Race Start Locations, and waypoints to get to them.
/way #2346 33.77, 76.24 The Heaps Leap
/way #2346 25.50, 42.13 Rags to Riches Rush
/way #2346 39.03, 28.69 Skyrocketing Sprint
/way #2346 39.22, 11.35 Scrapshop Shot

/way #2346 25.85, 41.69 Sweethearts Resort Ladder
/way #2346 39.94, 28.78 Skyrocketing Sprint Ladder
/way #2346 39.42, 25.92 Scrapshop Roof Access

These races are done with a jetpack. You only have 3 abilities in this mode; a toggle to swap between going faster or turning better (Just stay on going faster to get gold), restarting the race, or cancelling the race. There are both normal and reverse versions of the races.

Heaps Leap is on an elevated platform you can just jump on top of.
Rags to Riches Rush is on top of the Sweethearts Resort; to get up there go inside to the second floor balcony and use the intractable ladder there.
Skyrocketing Sprint is on top of a small building; there is an intractable ladder behind it to get on top.
Scrapshop Shot is on top of a building that you can only access by going over the top of the Scrapshop. Use the ramp to the side of the building to get on top and pass over.

Gold awards the Skyrocketer title.

I was unable to see the skyrocket timekeepers until I completed the Skyrocketing Sprint race first, then all of the other timekeepers became available. Not sure if intended or not.

For anybody as confused as I was. There is no introductory quest to Skyrocketing races. You have to go to 39, 29, near the Demolition Dome and start the first Skyrocketing Race named "Skyrocketing Sprint".

/way #2346 39, 29 Skyrocketing Sprint

Once you've completed it the remaining races unlocks. The time keeper is on top of the garage-looking building, you get up top via a rope ladder behind it.