Hopefully this can help people a bit. I just got it and it took a few tries. The Gold wasn't too rough, but I had to shave a few seconds off my original time to get it under 1 minute.
First - This Season 3, Episode14, Scene 4.
You will be driving the Cortina in a black and white "rally" stage (really it's just one of the courses reused in reverse from earlier in the season
).
In terms of hitting the sub 1 minute mark, you'll need to hold down the accelerator the whole time. In general, most achievements in this game require you to focus on not braking at all.
For the turns, focus on your drift. If you hit a wall, it is not the end of the world. However, your wall hits should be ones that don't decimate your speed. A glancing blow off a wall or two is not catastrophic. For the back and forth down the hill, one of the turns has no barriers on the outside of the turn. Going off the cliff will automatically mean you don't have a chance at the required time.
I'd recommend having around a 70 MPH speed down the hill drifting through the turns. I still usually hit a wall in there, but it was relatively clean.
One of the odder parts of getting the course down is the importance of actually being on what the game considers "the road". While the sides are quite far apart, your acceleration seems to be limited outside of particular portions of the track. You can easily get higher speeds sticking towards what they consider the road. Focus on this and it should help immensely.
I had to run it about 10 times myself to get the right feel for everything before I snuck by with less than 0.5 seconds to spare so don't be surprised if you have similar results.