Today I worked on getting rid of three medium size oil canning spots on the roof of my car. No oxy/acetylene torch so I used what I had which was a propane bottle. Things didn't go easy but I ended up getting it done.

When hammering on the spot do you to prefer to hammer before or after quenching? The guy in this video does it both ways.

https://www.youtube.com/watch?v=GN4RosIrEPg

And also I've been considering getting a shrinking disc and I'm wondering if it's good for fixing oil canning?

Shrinking disc works good. You poke your finger around the outside perimeter to find the spot that triggers it and then run the shrinking disc over it. You can also run it over the whole general area afterwards to tighten things up.