To ensure that the Billing administrator role can only be used for a maximum of two hours, you need to edit the role activation settings. To do this, follow these steps:
1. Sign in to the Azure portal.
2. Go to Azure Active Directory > Privileged Identity Management.
3. Click Roles > Role settings.
4. Select the Billing administrator role.
5. Under Activation maximum duration, set the maximum duration to 2 hours.
6. Click Save.
Once you have edited the role activation settings, User1 will be able to activate the Billing administrator role for a maximum of two hours at a time. After two hours, the role assignment will automatically expire.
Reference
Configure Microsoft Entra role settings in Privileged Identity Management
https://learn.microsoft.com/en-us/azure/active-directory/privileged-identity-management/pim-how-to-change-default-settings