How long does it take the apple service people to replace the recalled hard drive?
Hard to say. Maybe two to three hours.
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Normally, it takes some days but less than a week. If the hard disk your computer needs is in stock, the change will be faster and you may have your Mac running the same day or next day
The two to three hours means work time. It does not mean how much time you will wait until you can pick up the computer. That time, as mende1 states, is longer and will depend upon how busy the the service people are.
Retrieving data ...