I think they told me they start answering at 6am (Pacific Time) each morning. Not sure how late they answer.
However, if you are booking right at the Magic 30day mark, the schedule for those tours doesn't appear until 8am.
Today 9-4, I called for a tour on 10-4. I called at 7:55am and had to wait for 5 minutes. At 8am sharp the tour was there and I could book.