I can imagen four weeks is a good enough ... you can never be 100% sure, as we have seen... preventing exchanges from staking is probably the one important thing to look at, in the previous fork it was becouse Binance and Huobi staked their tokens the governance was taken over ...... but now for example Upbit has close to 150M liquid HIVE, and it they decide to stake it and vote governance, they can basicly overtake the chain... there is now a 30 days worm up period so to speak, newly powered tokens cant vote governance for the first 30 days, so this will give a heads up to the community, avoiding overnight changes, to ask questions why they are staking etc ..... the other thing to ask oursef as a community is how can it happen to have close to 30% of the supply be on one exchange! ......tldr, complex governance topic, multiple factors at play, I personaly dont mind four weeks powerdown....