Yea, a week grace period sounds fine.
And yea, I've seen corruption done or attempted on nearly every region we've taken over, plus a number of times my side doing it as well. It used to be something I would say a few times per year, at most, back before I deleted my account. But now it's almost systematic. You see that unitless noble just standing there during the TO, just waiting for his click battle...
Actually, yea, I think unitless nobles should risk capture during hostile TOs.
On way or another, I hate the mechanic.