do incall instead.... time constraints are never fun.

Do an in call with a girl who is already staying somewhere.  It's doubtful that you will be able to check in at noon.  You can always ask for an early check in when you book the room but most hotels won't guarantee that in advance.  You could luck out but it's a roll of the dice...

I have often meet at hotels either just before noon or after.  Sometimes, cleaning staff is on the floor but it's not been an issue.  
skb

Easily?  Book the room for 2 "nights". Check in after work on the first day and check out on the way to work on the last.

It is not the cheapest solution but perhaps you could find a second provider to see during the two day period to be less wasteful of the room.
Just look at it as the cost of having a rigid schedule that only allows you a noon window.

Another option is a hotel near a  major airport.  Tell the front desk you have a long layover between flights and need a place from noon until 4 pm to take a nap and do some work until your next flight.

Alot of 3 star hotels will let you check in anytime.At least here in Atlanta they will. I've encountered this problem many times when getting rooms. The more upscale hotels are stricter on the 3pmish checkin policy. For example, I have an appointment in the morning at 10am. I've had to call around and find a hotel that'll let me checkin at 8amish. So I'm kinda forced to have to get 3 star hotels then. Even though they're not as upscale as I'd like, I do make sure they are decent, clean, and in a good area. I'd never stay at a skanky run down Motel 6 type joint.