When visiting Charlottenburg Palace how long should one allow to see? Also is it close to other attractions in Berlin? Would be taking the U Bahn or S Bahn trains to get around. If the zoo is close can that be done in a day?
I haven't been to the Schloss itself, but in the buildings opposite the main entrance there are some small art museums that are interesting if you are into their specialism - the Brohan Museum (art nouveau and art deco), the Berggruen Museum (minor works by Picasso and Klee), and the Sammlung Scharf-Gerstenberg (symbolist and surrealist drawings and prints).
It won't take too long to get from the area to the Zoo by U2 U-Bahn.
It's a little bit of a hike from the Sbahn station of the same name, but there's a Ubahn station closer.
The actual walkthrough of the Schloss depends on how long you linger over the various audioguide details... if you've done a few of these, you know how they can sometimes go on and on about who designed and painted what room in what style with what materials obtained from what source, etc. Not listening to every second of the guide, I think it maybe took me 30-45 minutes to go through the building.
I wanted to spend more time wandering through the gardens and some of the outbuildings, but a heavy rain storm ended my efforts about half way through. Estimate anywhere from another hour to two to walk the grounds and see the other structures.
The Schloss is not that close the zoo, but along the same Sbahn line.