Someone_Else,
You will probably find that on weekends there are just fewer admin staff about. But I am sure someone else (not you obviously) will be able to show you around.
If you give HR a call they will probably be able to help you with contacts.
As for visiting loads of units; getting a broad view can't be a bad thing. If you visit Scottish, there probably isn't a dire need to visit another unit such as Swanwick (LACC) or West Drayton (LTCC).
Good luck with the interview
