I think I've had pretty good success with this. Since the parts are thin and the and heat time short, I didn't bother wrapping in stainless.
Preheat oven to 1,500F (oven is small and loses heat fast when door is open).
Set spring on heavy stainless plate, put in oven, and dial back to 1,475F.
From that point, cooked for 15 minutes including time for oven to come back up (about three minutes).
Pull plate and spring together, tilt the plate, and let it fall into the quench oil.
I let the oven cool back down on its own, then put the plate back into the oven with a heavy steel slug I had laying around to slow down the cool time of my little oven.
To temper, put the spring back in the cold oven, let it come up to 800F with the oven, soak for 30 minutes, then shut off oven and left everything overnight.
I tried a few variations on that. Cooking for ten minutes left the end product a little softer than I wanted. Cooking it for 20 made it extremely brittle prior to tempering such that my Rockwell tester shattered it. I tried a slower temper cool-down and that also made the end product much softer.
These numbers aren't quite right, but will give you some sense of the process. I just left my usual C-scale diamond in the Rockwell tester and I also don't have the right one for thin material.
In annealed form, it measured -25Rc, after 1,475 heat-and-quench it registered 35Rc, and after tempering about 30Rc. To contrast that with what five minutes +/- will do (without tempering), it was about 15Rc after ten minutes. After 20 minutes I couldn't even check it without the part shattering.
At any rate, I'm going to put the spring in service and see what happens. I think it's tough enough to handle the wear it will see and deflection is minimal, so I expect it to run a good long time given some of the torture I put my test pieces through.
If I can remember, after the spring has been in service for awhile I will report back with the results. It's a simple ignition component for a timer opened by a two-lobed cam.