She's the only one who knows when her next appointment is, after all. But I always took it on myself to monitor the time so I didn't get an unwelcome surprise.

I would agree it is up to the lady. I do get chatty as well with clients I like, so if we go over 15 or 20 minutes I think that is on me. If I am going to you and you booked an hour and I politely let you know I have to get going and you ask me to stay longer I would ask for my additional rate. I don't think you did anything wrong in the situation.

It's on her. I did a rare outcall for a one hour appointment. The young lady stayed 8 hours. Like in your case, she loved to chat and we had great chemistry. She was very low volume.  

I booked her again a few months later for an outcall and the same thing happened. Nothing was said about the over stay or the time.

You agreed on an amount, paid her, and that's all you owe her. End of story. And if it ends before I nut, that's on me, so I set my watch at the beginning. (Of course, I know it isn't the 'end of story,' there's always somebody with another view. But I ain't giving her a dime more.)

a provider say, “You’re paying for my time”?  I see that a lot in ads and web sites.  

 
So to be clear that I’m making every effort to stick to my agreed time, I do keep track, and when it’s getting close to “time’s up”, I use words and actions to let her know that I know.  And often she’ll say something like, “That’s ok, no rush”, so I’ll hang around if I can. Or she’ll make it clear that it’s time for me to go.

 
I also don’t let a provider use up a lot of time talking, unless it’s a long session and it’s someone I enjoy talking with, such as my ATF. I take the initiative to move things along.

When I go to her, incall... I monitor the time. When to start and when for me to leave. I never overstay my allotted time.
But when I have them come to me, outcall...it's on her when she wants to leave. I won't spend alot of time with the chit chat I normally get going kinda soon. So if all is going well then I ain't throw her out. It's all on her,after all mi case, es su casa.

specific amount of time.  It up to you to keep track of the time.  If you chronically overstay, you will eventually not be able to get any more appointments with her.  The gray area is if you are a generous tipper.  If you're a regular and she KNOWS you are going to tip her well, she will often extend the time without charging for it, instead depending on YOU to show your appreciation for the extra time she gave you on spec.  However, even in this case, when your time is up, you should remind her that your time is about up.  If she wants you to stay, she will invite you.  If she says she will see you next time, then leave.  If she has no other customers booked after you, she may invite you to stay for an extended social period just to have someone to talk to or a cup of coffee to share with you.  Follow her lead.