Is two factor authentication possible when using RDP with a Windows server, say by using a time dependent code?
Yes, it is possible.
If you want to have two factor authentication, which is naively supported by Windows, you could chose to use smart cards or virtual smart cards.
As far as I know, to get one time passwords for RDP authentication you'll have to use third party solutions. For example, you could try Duo security Duo Authentication for Windows Logon and RDP. Alternatively, as
paj28 pointed out, you could google another ready made solutions.
If you are asking for a time dependent code, you probably mean one time passwords based on the TOTP algorithm like the Google Authenticator or some hardware OTP token.
You can do so as alex pointed out with many different 3rd party solutions. Disclaimer: Mine in privacyIDEA which provides a backend system to manage the tokens and a privacyIDEA credential provider, which asks for the additional one time password which is verified against the backend.
As you need the backend to verify the OTP value, this will only work on-line. But as you are asking for authentication at windows servers, these are probably online and not running on your offline notebook ;-)