If you open a CMD prompt and type set, the environment variables available in this session are displayed.
If you then type @echo %date%, you will receive the same output that a date /t would have produced.
If you then type @echo %time%, you will receive the same output that time would have produced.
If you use Control Panel / System / Advanced / Environment Variables, you won't find date.
If you navigate to HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Environment or
HKEY_CURRENT_USERS\System\System\CurrentControlSet\Control\... the date environment variable is NOT defined.