It takes quite awhile (about an hour) to go from a crudely cut patch to a fitted one.
Once I'm satisfied that the patch fits as well as I think I can get, I'll hit it with two coats of weld through primer. Then fit it back into the cavity and get ready to weld.
As the various steps of grinding and fitting might bend the patch a bit out of shape, I pick a section to begin the weld and tack in a few inches of it. I'm most likely going to need to hammer another section back into shape so I want it fixed at one point.
