WBC has restricted stays during peak seasons -- 3,4 or 7 night stays required during peak periods with check in/out on Friday, Saturday or Sunday. But Prime Season is only 17-18 weeks per year.
"Orphan" nights are sometimes available. If two guests book the same room for 3 nights each, that leaves one "orphan" night and you can book those if they are available. That doesn't mean the particular night you want will be one of them, but one-nighters are available sometimes.