They usually keep a couple of loaners for emergencies. Since this is a routine/ non-emergency appointment, there's no reason to fret. The 1200 mile service is +/- a few hundred miles. Unless you plan to put 1K+ miles on your car before the 28th, I wouldn't worry about it.
Current: 2016 F80 M3 SO | AB XT1 | ZCP | etc.
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