Tyler, George and his helper showed up on time to start the job (rare among contractors!). Tyler confirmed the measurements I gave him and confirmed the price and duration of the work in a few minutes. He confirmed that my ceilings (3 rooms with 600sqft in total) were painted, making the removal/patching harder. The whole process took (as they well predicted) a total of 3 days, 2 half days of scraping, then plastering, 1 break day to dry and painting on the final day.
The only minor flaw we noticed was that the crew painted the newly finished ceiling together with a portion of the crown moldings, which caused the crown molding to have 2 different tones of white. It would be best to avoid re-painting the crown molding at all (just the new ceiling) or re-painting it completely to avoid this, but luckily it is not clearly noticeable.
Plastering such a large area is definitely not an easy job and they did a really excellent job smoothing the ceiling out. The ceilings now look MUCH BETTER!