I'm running into this the MSP Spring Hills Suites (Eagan).

Try to book April 16-17 (Thurs-Fri): rooms available.
Try to book April 16: sold out.

This one is even more head-scratching than the Burbank Marriott. The SHS Eagan a standard suburban property that does a mix of airport business and presumably some local business travelers as well.

There is no unusual demand in the area that week. Every nearby Marriott is selling rooms at typical rates. Weekday rates are their usual $120-140 for all the midrange brands. Weekend rates are the usual $75-100. This SHS is the only one with the April 16th quirk, and I can't figure out why.

If we have to stay somewhere else, fine. I just wish I understood the logic, because we actually do prefer this particular hotel. I wish Marriott had a better answer than "sometimes hotels have minimum stays." Yes, of course they do, I just question whether this particular airport hotel intends to on this particular night.