Yes, most exchanges always turn off wallet deposits/withdrawals 2-3 days before intended fork date. Then wait a day or two after fork to see if the chain is stable and then update their own node (larger exchanges tend to run an own node for each chain). If the fork requires an additional replay, it will further delay when they re-activate withdrawals/deposits. 

That's very much industry standard. So if you buy or need an upcoming transaction and you know there's a HF coming... do it while the exchange wallets are still open.