Here is the issue.   We are a global organization with support teams around the globe.  

1. We have some groups that follow the sun, that would fit for setting an SLA for all those as 24/7 and for the SLA would it make sense that timezone in the SLA be configured for GMT?   See Image:
2. Then we have support groups who work thier workday for different regions.   Do we set up SLA by Region to accomodate those?   And how do we account for Holidays that affect working weeks?