Fixes https://dev.azure.com/mseng/TechnicalContent/_workitems/edit/1998755

Author: ggailey777

articles/azure-functions/functions-premium-plan.md

@@ -18,7 +18,7 @@ Premium plan hosting provides the following benefits to your functions:
 
 * Avoid cold starts with warm instances.
 * Virtual network connectivity.
-* Unlimited execution duration, with 60 minutes guaranteed.
+* Unlimited execution duration, with 60 minutes supported (outside of platform upgrades and outages).
 * [Choice of Premium instance sizes](#available-instance-skus).
 * More predictable pricing, compared with the Consumption plan.
 * High-density app allocation for plans with multiple function apps.
@@ -143,7 +143,13 @@ To learn more about how scaling works, see [Event-driven scaling in Azure Functi
 
 ## Longer run duration
 
-Azure Functions in a Consumption plan are limited to 10 minutes for a single execution. In the Premium plan, the run duration defaults to 30 minutes to prevent runaway executions. However, you can [modify the host.json configuration](./functions-host-json.md#functiontimeout) to make the duration unbounded for Premium plan apps. When set to an unbounded duration, your function app is guaranteed to run for at least 60 minutes. 
+Azure Functions in a Consumption plan are limited to 10 minutes for a single execution. In the Premium plan, the run duration defaults to 30 minutes to prevent runaway executions. However, you can [modify the host.json configuration](./functions-host-json.md#functiontimeout) to make the duration unbounded for Premium plan apps. Your function executions can have an unbounded duration, with the following exceptions:
+
++ Platform upgrades can trigger a managed shutdown and halt the function execution.
++ Platform outages can cause an unhandled shutdown and halt the function execution.
++ There's an idle timer that stops the worker after 60 minutes with no new executions.
++ [Scale-in behavior](event-driven-scaling.md#scale-in-behaviors) can cause worker shutdown after 60 minutes.
++ [Slot swaps](functions-deployment-slots.md) can terminate executions on the source and target slots during the swap
 
 ## Migration