This year we implemented the SLAs feature to help manage the increasing ticket load, however this is complicated by differing timezones, contracts and business hours.

We only use the first reply time metric, but this is decided by a combination of:

Contract (gold, silver, bronze, custom)
Priority (urgent, high, normal, low)
Timezone (if appropriate dependent on contract)

To achieve this, we needed to use a combination of:

SLAs

We use 4 of these - one for each contract - gold, silver, bronze, custom. We then utilize the "First time reply" target and the "Business hours" option, setting the appropriate values for urgent, high, normal and low.

Schedules

These were used to factor in different timezones. One for each different combination of contract and timezone, e.g. bronze (tz_gmt). Then the working hours (e.g. 0900-1700) were adjusted to match the contract and timezone.

Triggers

These were needed to apply the combination of SLA and Schedule onto every new ticket - one for each contract/timezone. We used the appropriate contract tag to set the relevant schedule.

Now our "Unassigned Queue" is managed by the "Next SLA breach" so we never miss an SLA regardless of Contract, Priority or Timezone.