If you are planning to move your Bitcoin to Coinbase, you can do it anytime before the hard fork. But don't leave it for the last hour, because the fork may occur before than it is planned, and Coinbase will suspend deposit and withdrawals some hours before the fork.
If I decide to sell my B2X after the fork, maybe I move my BTC there, so I can sell it as soon as possible, because looks like it will be launched with about 15% of Bitcoin price. I don't believe It will have a price higher than that soon, but I'm still not sure whether I'll hold both BTC and B2X, or whether I'll sell my B2X and buy more BTC to hold.