What's the difference between 'for the last four days' and 'for the last four days' when they are used with 'Where have you been'?
Where have you been for the last four days?
Where have you been in/within the last four days?
The first implies you've been one place for the duration. The second asks you to list all the many places you have been over that time period.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.