Most every hotel I have been in lately (I travel often for business) have some type of express check out where you can simply leave the key(s) in your room when you vacate and do not need to return to the front desk. This is provided that your room is prepaid, usually by credit card, and you have no need to settle any expenses charged to the room.

Several hotels I have visited recently also have "day rates," intended for a short stop, say for a shower and a nap.  They tend to be near major airports, and the rate is about 60% of an overnight stay.  Early check-in is expected (though not always guaranteed), and early check-out is mandatory.  I've found out about the rate by calling the front desk of the particular places I'm interested in -- they don't show up on their internet sites -- and indicating I'm passing through on such-and-such a date, and need a place to take a quick nap, shower, shave, and change clothes before (take your pick -- a business appointment, moving on, etc.).

Try it, and good luck!

Paul

A friend who used to be in teh motel business told me that generally motels/hotels actually like "nooner" customers because they can rent the same room out more than once in a day.

The moralizing management would probablybe the exception rather than the rule. Just play it cool.