@Kan Kok Keong - Welcome to Microsoft Q&A and thanks for reaching out.
You must have certain permissions to enable VMs for the Start/Stop VMs during off-hours feature. The permissions are different depending on whether the feature uses a pre-created Automation account and Log Analytics workspace or creates a new account and workspace.
You don't need to configure permissions if you're a Contributor on the subscription and a Global Administrator in your Azure Active Directory (AD) tenant. If you don't have these rights or need to configure a custom role.
Once you have the role added, create a scaling plan with Name, location and TimeZone.
Then Select Add Schedule and provide the details for Repeat Mode meaning which days you would that like to repeat.
For more information on this, please refer to the below document: automation-solution-vm-management
Hope this helps.
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