I understand it's frustrating having to wait around, but sometimes it makes sense to do the long privates early. Sometimes a long private can't be helped. You're haivng fun, conversation happens, maybe takes too long to finish.
When I'm not camming myself, there's only one model I do privates with. We do our privates straight away, before the room gets busy. It makes sense because, if she's on for a while and the room has a lot of tippers, especially whales, going private can be a loss.
Me, I'm not too picky about when I go private because my room is generally slow and I'd typically make more in a private.