I voted 8 week but really it should be 5 Weeks, only because of the 30 day account recovery window though. If we aren't to bothered about the powerdown time being a method to protect funds from being raided in the event of a hack then it should be 2 weeks.
It can't be instant, 3 days or 1 week because of the interactions with reward pools, voting etc.

^{I'm a hive witness supporting the blockchain please consider voting for me.}