You'll have to do at least one fitting (preferably two), so I should think you'd need to be in BsAs for at least several days to a week or so. Shipping shouldn't be a problem, what with DHL and FedEx in town. The great thing is that once they've made your last (the model of your foot), you can simply order shoes whenever you want -- I did just that for my father-in-law.

On a side note, Correa is a pretty old-school place: no credit cards are accepted, strictly (Argentine) cash only.