I don't know. I know that I ask my T for an extra session and she lets me know within at most 2 hours. I think I'd feel forgotten if they didn't get back to me by the end of the day (non business just day). I take the "I'll get back to you" to mean they need to look at their schedule and possibly move someone or something and that could take time to see if they can get an opportunity for you to come in. Just what I think though - I could be wrong or very needy needing to hear back so soon.