I just saw something similar on the Marriott booking website. I was searching for rates at a specific hotel for a Wednesday and Thursday night stay, but the website showed me a rate that apparently required a weekend night. When I clicked to see the rate rules, it clearly said that the stay must include a Friday or Saturday night. I didn't take the rate so I won't find out what would have happened upon arrival, but it looked like I would have been able to book the rate. BTW, it was an AAA Hot rate where the regular AAA rate was cheaper, so I was checking the rate rules to see what perks (none in this case) like breakfast or valet parking might have been included.