There is no concept of shared work schedules when creating services in Dynamics CRM. So if you have a large garage with a resource group containing all your mechanics and they all work the same hours the expectation is that you will enter the working hours for each individual mechanic which is a bit tedious. 

A way around this is to create a facility/equipment resource for you opening hours and set it's work schedule to your working hours. The important point when doing this is to select the show capacity option and increase it's capacity to a suitable large number.

You can then use this as a resource in your service and it's work schedule will be used when scheduling however as the capacity is set so high there are no constraints on scheduling multiple service activities at the same time.

You now only need to enter the time off records for mechanics which makes maintaining work schedules easier.