Block hour when an employee got a service

I have the same employee for 4 services. When someone book one service for example "massage" from 9 to 10; I need that the same hour and day in the other services be "not available", as the same employee can´t do 2 services at the same time.
How can I do that? I can´t configure it!

Im using Joomla. 2.5.9 / Os service 1.4.0 - last version (downloaded today)

Hi,
Please go to backend, configuration, tab Booking Configuration and uncheck "Employee can work in multiple services in the same time"
Thanks
Dam