Long enough to fix the corporate records and confirm the qualifying year, which is usually months rather than weeks. The petition itself is the shorter part.
Plan around the slowest dependency
The realistic schedule is set by whichever of the underlying facts needs repair. If the ownership chain is clean and the transferee has an unbroken year on the right payroll, preparation is quick. If either is untidy, the timeline stretches: a corporate reorganization has to be documented properly, and a broken qualifying year cannot be shortened by any amount of effort, only waited out on a corrected arrangement.
A new office is normally approved initially for one year, which means the operating plan must be capable of showing real progress within that period, so the premises and hiring commitments have their own lead times. Build the calendar from the corporate side first and let the filing date follow it.