If you really want to do justice to Bletchley you need
two days.
I did the site (three museums, plus the actual Bletchley house) in
about six hours. They threw me out when I mentioned B-Deinst, but I
was done anyway.
Less than three hours is really not good - you would miss too much,
especially the demos.
Bill, with your time constraints, go into London and spend the time at
the V&A. Completely worth it.
--
Will