Hyatt apparently loves these short term sales every couple of months. This time they are offering up to 30% off of 108 properties in United States, Canada, and the Caribbean. These are prepaid, non-refundable, and non-cancelable. Diamond members can use their suite upgrades on these rates, subject to availability of course. These rates need to be booked by midnight on 21st of December.
The following Hyatt web page has the list of all the 108 participating properties and the terms of this offer.
Sometimes these rates “work” and sometimes they don’t. You get a lower price but you give up the flexibility. I would only book the sale rate if my plans were absolutely set in stone.