While this question is rather old and originally concerned Windows 7 it still has relevance on Windows 10.
So you need to automatically log in to a specific user, triggered by external means - be it a timer or a connected device, it doesn't matter for the purpose of this answer.
The textbook solution is to roll your own credential provider which calls upon ICredentialProviderEvents::CredentialsChanged when the device reports its ready state - or the timer elapses - and then adds in his own credential for the "kiosk user", marked as the default selection and autologin to facilitate automatically logging into the system.
As an added measure you can hide away the default credential providers using ICredentialProviderFiler to restrict logins even further.
Similar scenarios are alredy in use with logging in using biometric means or unlocking the system using a NFC or Bluetooth device.