Tente isto:
SET "ADJUSTEDTIME=%TIME: =0%"
IF "%ADJUSTEDTIME:~0,5%" GEQ "19:58" GOTO :SHUTDOWN
IF "%ADJUSTEDTIME:~0,5%" LSS "08:58" GOTO :SHUTDOWN
GOTO :EOF
:SHUTDOWN
MSG * "Your device has not been authorised for use at this time and will now shutdown."
SHUTDOWN -s -t 120