What matters obviously is how many cars can they roll out in a day. Sure, from the time your car starts to the time it rolls out is 24 hours, but how many other cars came out in the same day? If the average daily demand for custom vehicles is significantly higher that the daily production capacity you get long wait times just because the job queue is backed up.

So yes, 'manufacturing time' is likely not the issue, it's 'manufacturing capacity' that will bog you down.