Straight-line and the mid-month convention
Buildings depreciate straight-line: depreciable basis (purchase price minus land) divided by 27.5 years for residential rentals or 39 years for commercial property. The mid-month convention treats the property as placed in service at the midpoint of its month, so the first and last years get a half month plus whole months, never a full year. The day of the month you close does not change the schedule.