By default, Azure functions timeout after 10 minutes (or 30 minutes if running in an App Service Plan, or a Premium plan).

The official documentation (see https://docs.microsoft.com/en-us/azure/azure-functions/functions-host-json#functiontimeout) says that you can increase (or reduce) this by adding a functionTimeout value to host.json.

But this doesn't currently work for a .NET 6 Azure function (v4)  (the latest version)!

Instead, (my thanks to https://github.com/paulbatum who disclosed this trick on https://github.com/Azure/azure-functions-host/issues/6111) adding this setting AzureFunctionsJobHost__functionTimeout in app.settings.json (or in Configuration in the portal) works, e.g. for 23 hours:

"AzureFunctionsJobHost__functionTimeout": "23:00:00"