Why not just change AND to OR? In that case when the hour of the day is greater than 20 then it will fire. if the hour of the day is less than 6 it will also fire. Look at it less of the time frame when it needs to fire and more of a time frame excluding those hours when it does not need to fire.
If Hour(Now()) >= 20 OR hour(Now()) < 6 Then
//RUN SCRIPT
Else
//RUN OTHER SCRIPT
End If