Rust Rust Formation

On average, how much time for rust to form?

A couple of weeks ago, my car slid on the ice and I hit the guardrail front-on. I don’t remember the back portion of the car hitting the guardrail as well, but I was very stressed at the time.
This was about 1 month and 2 weeks ago, and I got the car to a shop on monday. Rust hadn’t formed then.
As I picked up the car again today, I saw they had washed the car. With all the dirt removed, I noticed another bump and scrape on the back portion of the car. This bump, on the other hand, had very visible formations of rust, almost covering the entire scrape.
So, I am wondering, as rust hadn’t formed on the frontal bump-and-scrape, could this have happened at the same time? Or does rust take longer to form?
The reason I’m asking is, this is my father’s car, and I’m wondering if I could be responsible for this scrape as well, even if I don’t remember it.
Just FYI, I live in Norway, it has been quite cold here and they use salt on the roads.
Thanks!

I would assume that the scrape you are talking about is an old one. If the other damages done to the car had not rusted yet, then this scrape is a bit older than the other damage. Possibly the car was backed into a pole or possibly into another car? It depends on certain conditions for rust to form. If you have exposed metal in the winter and salt gets on it, surface rust forms almost immediately. It takes water and oxygen exposed to bare and untreated metal to form rust. Your best bet would to either take it back to the body shop and ask them to take a look at it or ask your father, clean up the rust by a wire brush then primer over it and then you can use a body filler when the weather is a bit nicer. I hope this helped. Good luck.

RUST FORMATION IN PUMPS