The last time I needed my Aerospace battery changing, I took the watch in to the Breitling place in London. They explained that it would take about a week, as they do a 'power soak' test as well as simply changing the battery etc.
If you take it to a reputable Breitling dealer they will tell you the same. And it'll take longer as they will need to pack it and forward it.
I wouldn't recommend letting anyone but an authorised Breitling dealer touch your watch!
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