I recently saw an ad that listed a rate for clients that know they don’t need a full hour to attain their complete satisfaction; probably somewhere between 30 and 45 minutes. Is this provider offering a desired service?

..about less than an hour long sessions. Speculation about demand for quicker date durations isn't necessarily useful. Companions who cater to clients seeking those experiences will let it be known. Companions who do not do shorter dates will not regardless of the fact that they know there are interested clients.  

 
Over the years, I've seen one companion who advertises that she offers 45 minute sessions. That strategy is seemingly successful for her. I'm sure it's popular and I love that for her. Generally though, prorating dates by 15 minute increments can be very cumbersome. Doing so can create more problems than it solves. There are valid reasons why it'll be hard to find providers navigating in this way unless you're looking on STG, etc.

It isn't a question of whether it's a desired service as that has been well established for ages. The question is how desired is it, and on that front I have no idea. lol.  
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For some men seeking short stays, it's a lack of time issue. For others, it's a lack of money problem. Some men may even be extraordinarily introverted or shy, and might feel intimated by chatting with a hot woman, and with dates of those lengths, that becomes a non issue, or certainly less of one.