Document business hours (#46)

tiers.mdx

@@ -21,3 +21,9 @@ When configuring an SLA you can set when you want to be warned of a breach. For
 SLAs can also be driven by priority of threads. This allows you to have a different SLAs for "Urgent" vs "Normal" priority threads. If you have configure multiple SLAs for the same priority then only the first SLA will apply.
 
 If you want to create a 'default' SLA then you can need to first create a tier and make that the default in your settings. Then you can configure SLAs like you would on any other tier.
+
+### Business hours
+
+By default SLAs apply at all times. They can be configured to only count working hours by toggling on **Only during business hours**.
+
+To configure business hours go to **Settings** → **Business hours**