Our client has offices in various countries. Although they have regionalized support many of the applications are centralized & inter-related.
A user in Sydney has to use an application in the UK or the US & if that particular application or server may be down, they would raise a ticket. But as it would be off business hours in the UK or the US, the support technician will not attend to it & hence, the ticket would breach SLA.
In order to prevent the SLA from being breached, we need the SLA agreements in HPOV to be customized such that the SLA would be based on the assigned support technicians (workgroup) business hours. Hence, in this case the SLA should start from US time 8 AM (assuming the technician is in US) & continue till 5 PM.
Also, the same ticket may get assigned to another technician in UK if there is a dependency. Hence, the ticket should then continue the Service level target only during the UK business hours once it is assigned to the workgroup based out of UK.
I think you should create an Organisation for the UK based support group and one for the US based support group and assign those organisations the appropriate time zones.
Then create separate Service Level Agreements. Enter the new Organisation as the "Provider" and in those SLA's specify that the "Applied Time Zone" is that of the provider organisation.
You could then have a seperate Service for each support group, which will use the relevant SLA, (the ones just created).
Then when a call is raised which uses that Service, the Deadline will be calculated using the correct time zone and taking into account eh support hours of the relevant support group, either USA or UK.