I can say that you do have a time limit to confirm a lesson: one week, if I'm not mistaken. If the student does nothing and the time limit expires, then the credits for that session automatically go to the teacher. If there was a problem with the lesson, the student has a chance (one week) to say that there was a problem.
Still, I'm not sure if that answers your question, because your question wasn't very clear. It's best to write to italki support about this:
There's also an email link on the page with the session details.