Look at the Hyatt Points Chart on the website for the checkin days at the different resorts. Some resorts have weeks with multiple checkin nights(Highlands Inn and Piñon Pointe for example have Friday, Saturday, and Sunday weeks checkins).
For Friday checkin weeks the three day weekend stay checkin is Friday. For two day midweek stays it is Monday or Wednesday. For four day midweek stays it is Monday.
For Saturday checkin weeks the three day weekend stay checkin is Saturday. For two day midweek stays it is Tuesday or Thursday. For four day midweek stays it is Tuesday.
For Sunday checkin weeks the three day weekend stay checkin is Thursday. For two day midweek stays it is Sunday or Tuesday. For four day midweek stays it is Sunday.
The above is for the legacy program. HPP has checkin any night.
Hope this helps.