I did it w a buddy. Took us about 6 hours, but the first side (drivers) took 4.5, and the other took 1.5, once we figured out how to do it. If it's a competent shop, I would think 5 hrs max plus alignment. That's for an x-drive, which is definitely more difficult.
2012 550i xDrive, DG & Black, M-Sport, ARS, Conv, Lux, Cold, HUD, Prem Sound, SAT.
Dinan Stage 2, springs, M5 mufflers, and 303M/Michelin PSS