Day rental of hotel rooms is fairly common now, especially for business purposes - especially in downtown and urban areas. I've booked day use for both business and personal, and honestly the hotel staff could care less and would not even inquire about the purpose of you wanting a day rate. There are two main sites in Denver - dayuse.com and hotelsbyday.com. There isn't a large selection of hotels, but they are name brand hotels.
Another option is to go to the Hilton, Marriott, Hyatt, or Choice hotels websites and select a day use option (if available) when you go to book; you can also call the hotel directly and ask if they offer a day rate...many do despite not being advertised.
A third option that I've found that works quite often is joining the rewards program for large chain hotels like Marriott Bonvoy or Hilton Honors, and then just booking a room like you normally would. Check-in is usually 3pm and then you can request a late check-out - which is usually free if you are a member of that hotel's rewards program. So essentially you are getting the room for nearly 24 hours.
Another hint - try to find a place that has online check-in with a mobile key option. That way, you can check in remotely and get your room key on the app without having to go to the front desk. This is great for when you want to use the room between early morning hours and say noon or later with a late checkout without having to worry about checking in the day before, and also not worry about your room being canceled because you didn't show up before 10pm.
Hourly hotels don't make sense to me...they are usually janky places, and I would not want to meet a date there anyway. Have some class, right?!
