"How can I change the employee hours? The hours are grey and do not change..."

Usually this is because you need to adjust the business hours to extend the hours that the business is open to allow the employees hours to then fill the business hours.

You can set the employee hours by clicking on the employee name at the top of the main booking area and then selecting "Edit <employeename>"

More information about changing the business hours can be found at:
http://diarybooker.uservoice.com/knowledgebase/articles/112502-how-to-change-the-business-hours