We want to see how you think about putting code together and how you think about trade offs.
Home: You can do your coding exam from home. Lots of folks prefer their home environment. Questions can be asked over email (though preferably in batches as needed).
In Office: You can come into the Qwilr offices and take the coding exam. You'll be setup in one of the meeting rooms (they are nice and comfortable, air-conditioned and well lit :) This way you can ask any questions you might have, by just hopping over to a Qwilr engineer and getting some input - and you'll get a feel for the space.
Note: There is no preference on Qwilr's side as to which of these you choose, it's all about being relaxed, so you can give your best effort.
There isn't a specific "time limit" to this task - its a case of build what you can within a timeframe that seems reasonable to you.