Re: 3hrs in IMAX?
You're the one who doesn't seem to be getting it. When a major motion picture is released "in IMAX", it means they're being played in traditional theatres branded by IMAX. It does not mean that it will be shown in purpose-built IMAX theatres on actual IMAX 1570 film.
So yeah, OF COURSE there's no sign of Interstellar being shown at your local science center. Nobody ever said it would be!
By the way, does the UK actually HAVE a legit 1570 theatre?