@san I tested your scenario to see what might be happening when a user logs into teams app, the Microsoft office suit apps prompts the user to allow them to manage the device on which they are trying to sign into, they will see a prompt like this :
If the user clicked on OK (which most users do) the device gets Automatically registered to Azure AD. In my case it was instant within few seconds.
Azure AD use the device to implement Conditional access (use device authentication) if any and also to maintain single sign on for the device.
If your device had some delay, the event logs under User Device Registration (Event Viewer -> Applications And Service Logs -> Microsoft -> Windows ->User Device Registration) might tell what was happening, under normal condition, it is instant.
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