I am wondering where you find STOPOVER rates ?

I can tell you that on the day of travel that you can call AIRPORT ACCOMODATIONS at 800-935-5995, and tell them you have a pink ticket from United Airlines, and you will get a deeply discounted rate ($70 to $95 at Marriott, Hilton, Hyatt, etc.)

The "pink ticket" is never checked, but I do not think you can call to make a reservation until the late afternoon of any given day. I think they resell any unused hotel rooms near major airports.