Time minimum-While not universal, the ladies most interested or capable of this have a longer time minimum. This can be anywhere between 90 minutes to 4 hours. These are ladies who know what they are offering is different, and aren't compromising to be everything to everyone.
Rates-How deep is the per hour price difference between her minimum and, say, a day or a week? This sort of incentivizing not only shows that she's "walking the walk" of her preference, but chances are pretty strong that she's also pulled in a larger percentage of longer date gentlemen who recognize that they are her preferred audience, which means she's likely to have more experience in that area (which means, of course, that you are far more likely to have a more seamless, enjoyable experience

).
Reviews-This can be a tricky one, because many gentlemen who engage in longer dates simply do not post reviews (and even fewer post on these boards, which may make gentlemen recommendations for your question slim). That said, there are enough who do, and those can give you an idea of whether the lady in question has experience in that area, and how she conducts herself in those engagements. This can mean both whether she is the type of girl you'd want to be seen in public with, and also whether her "style" matches yours with regards to longer date. Even with reviews of shorter dates (her time minimum, whatever that may be), reviews of ladies more geared toward longer experiences should read more like a date, rather than a physical description followed by an alphabet soup.
Unfortunately none of this is easily plugged into a search engine, but with a little homework, it should greatly help you narrow down your options!
Best of luck!