Monday Hour One & Client appointments

In my coaching business I offer prospective clients a 45 minute call with me which they can schedule by accessing my calendar. I usually have three full days open from 9 until 5 to give clients maximum flexibility. These calls are where I enroll new clients and therefor it is a key part of my sales strategy. How does the idea of Monday Hour One fit with this as I only know if a call is booked 12 hours in advance. They could quite easy book a session when I have focus time scheduled or free time.