I work in a very large medical company were they throw around words like kaizen, lean manufacturing etc... I'm on the engineering end and always laugh when some big exec throws out some ludcrious completion date. If design freeze is like ours, everything is developed by the time it starts with only minor tweaks to product and the actual equipment. To reach design freeze could take 2 or more years. I would be more interested in the time it takes from the drawing board to actually producing cars. We should also remember Toyota isn't making any brand new vehicles, it is just tweaks on an existing design, and really just a bunch of boring vehicles.
Also trying to rush a product into production you run the risk of recalls because somewhere along the line somebody cut a corner to save their ass from missing a deadline. It takes a pretty thorough document control system to prevent this. It becomes even harder when you have multiple plants producing the same product.