根据条款
v. 4 p.m. Late Checkout. Platinum Elite Members and above may check out as late as 4 p.m. local time of the Participating Property. Members can request late checkout when making a reservation through central reservations, at check-in, via the mobile app (where available) or at any time during their stay. At Apartments by Marriott Bonvoy, Platinum Elite Members and above are guaranteed a late checkout up until 2 p.m. local time and may request to check out as late as 4 p.m. local time based upon availability. This benefit is guaranteed at all Participating Properties, except at resort and convention hotels and Design Hotels, where it is based upon availability.
我的理解是除度假、会议酒店外,延迟4点退房这项会员权益是保证提供给会员的;即白金及以上会员可能的最晚退房时间是4点,但没有保证一定延迟到4点退房。不过国内普遍厚道,大部分都可以延迟到4点。