With the new WoH card, your statement close date will only affect when the nights post to Hyatt, but not which year the nights count toward. With 2018 as the only data point we have, all spending that occurred in 2018 counted to 2018 qualifying nights, regardless of whether it was after your Dec statement closed. So if your Dec statement closes early, you still have until the 31st to spend for qualifying nights. From the other perspective, don't spend after your Dec statement closes expecting it to count toward the next year's qualifying.