how to stop online booking from creating additional future appointment times in one day

Hi guys is me again... sorry for the second question, but I really would like to keep this and get it up and running.

How can I eliminate or stop the system from creating future appointment times in one day? For example we are open from 8am-9pm, some of our services are 4 hours and others are 7 hours, but we would only need one appointment time for each service per day... In the summer months we can run two for the 4hours services because our days are longer, but in the winter months we can only run one of each, per location ...

Please advice.

Thank you much,
olga_i@sbcglobal.net