About how many hours do you need to see all of the exhibits?

1 to 2 if you aren't interested in attending any of the shows. However I would highly recommend them.

3 to 4 if you attend the shows

2-3 sounds about right.

I would recommend 2-3 depending on whether or not you have kids, if you want to see specific programs, if you want to cover EVERY inch. I'm a local, go every couple of years, usually by myself and I take 2 hours.