Usually leaders stay at Blair House, but this time he actually chose the Waldorf. Not sure if the General Secretary didn't finish using his FN, or if he got influenced by all the churning talk.
Last time I stayed there, they gave out tons of glass-bottled water, and I couldn't even get through security at many attractions carrying them.
Water in glass bottles may indeed fail security checks at some venues. If you're just keeping it in your room to drink, it's no problem—as long as you don't plan to bring it into attractions that require bag inspections. If you really want to bring some, it's safer to transfer it into an ordinary plastic bottle.
For accommodation at this level, how far in advance is it usually finalized? How likely is it that the hotel could be changed at the last minute?
The hotel itself is open to the public, but when an important delegation is staying there, floors and elevators are often placed under temporary restrictions. Ordinary guests may not notice anything until they suddenly find they can't get into certain areas. To the outside world it's a hotel, but internally the security logic is much like that of a sealed-off compound—so don't judge the level of the reception by brand tier alone.
The key isn't which hotel they stayed at, but whether the choice itself sends some kind of signal. If they deliberately avoided the traditional state guesthouse, it might suggest the protocol arrangements were more flexible; if it was simply a matter of the room or the size of the entourage not being suitable, then it's purely a logistical issue and there's no need to read too much into it.
Is the check-in time based on the local date or Beijing time?
I'm a bit hesitant about equating a hotel brand directly with the standard of reception. It's true that Waldorf Astoria is often used for high-level receptions in many cities, but security and concierge arrangements can vary widely between different properties of the same brand, different floors, and different time periods. Without specific sources, it's hard to infer the considerations behind it based on just a name. If we really want to discuss it, it would be more prudent to wait for more verifiable itinerary information before drawing conclusions.
If this really were arranged according to diplomatic protocol, the Waldorf and Blair House differ quite significantly in nature: the former leans more toward a commercial hotel that can operate for the public, while the latter is closer to a state guesthouse. To verify this, you could pay closer attention to whether subsequent official itinerary releases mention the meeting location, or compare the scope of security road closures during the same period. These details can tell you more than simply looking at which hotel they stayed at.