Rooms.aero is another one you can filter to all Hyatt properties in Mexico and then search availability for X nights including X days (up to 5 nights)

Edit to Add: For example I was able to select 4 nights and Mexico and it shows the Andaz Riviera Maya is available for 4 nights. Then I changed to 3 and my start date to 12/30 and it shows suites available at a few different resorts. So if you're willing to split your week 4/3 you can get some cool places. 7 nights in a row that time of year might be tougher to swing.