They have some morning to afternoon rooms at hotels in the city, though they may not be much cheaper than typical overnight rates.
an anyone tell me how to go about getting a hotel room for a few hours?
All the travel/hotels websites requires at least 1 day stay.
ALSO how to book it with alias?
but you can always inquire.
In most cases you'll have to pay for a whole day even though you are not using it for more than a few hours.
Book a day, and leave when you want, they will not know.
As far as booking with an alias, you're on your own. You will probably have to use a credit card to secure the room, so using an alias is out. However, the provider who is visiting you does not have to know that.
LLAP,
Swim
This a very regional kind Q and I know that maxdogooder posts to the NYC board (as do I). So, I'll direct him (and anyone else) to recent discussions on the NYC board.
Can anyone tell me how to go about getting a hotel room for a few hours?
All the travel/hotels websites requires at least 1 day stay.
ALSO how to book it with alias?
Even in NYC, it seems that the truly anonymous short stays are disappering. See the recent NYC thread. Years ago, you could register at the Liberty and the only ID you needed was a picture of US Grant or a couple of Jacksons to vouch for you. Now they require a real picture ID (and I assume that they write down the info).
The NYC thread has some other suggestions on how to search
....tend to offer hourly or half day rates, mainly targeting travelers who may need an hour or two to freshen up and wait out a layover.
Just leave the keys in the room with a tip for the maids and leave when you wish. 
The bigger issue is finding a hotel between noon and 2:30/3pm, but as Lopaw mentioned, some hotels (esp. around airports) will let you check in early for an extra fee; just check online or call in advance to make sure this is an option.
Thanks for the info,
I always had the problem of using the room for a few hours and then driving back to the hotel the next morning to check-out. I never thought of leaving the keys with the maid and tipping her. I thought I had to physically check-out without being charged for an extra day if I didn't check-out by noon.
I very rarely ever "check out' of hotels here in the US. I just leave, usually they will slip the receipt under your door very early in the morning so you can make sure there are no discrepancies in the bill. So all you really need to do is leave. No need to even bother with the key/s unless you are staying in a VERY old hotel that still uses actual keys. Modern "keys" cost less than a penny apiece and the hotels go through thousands of them.
Welcome to the 21 century. lol
They have some morning to afternoon rooms at hotels in the city, though they may not be much cheaper than typical overnight rates.
Use the room twice....once in the afternoon, then again the next morning. You don't need to physically spend the night.