A powershell workflow runbook, "Stop-Start-Azure-VMs", and a powershell module, "AzureVMAutoStopStart".

The runbook should run under a schedule within an Azure Automation Account, and uses the module to determine, based the subscription and tag names supplied, which VMs should be stopped or started. The tag should contain the times and days a VM should be stopped. If the runbook is executing during one of these periods, the VM will be stopped (if started). Otherwise the VM will be started (if stopped).

The tag must be in the format HH:mm-hh:mm|ddd[/ddd][,...n]. So, a tag may look like any of the these: