i'm not sure build time is all that important. What matters is cars per hour coming out of the door. if you have 100 cars on the assembly line and it takes 18 hrs to build one then you're turning out 133 cars per 24 hr day.
Here's how the math works... each car is a 1/100th of 18 hours, or 10.8 minutes apart. There are 1440 minutes in a 24 hr day, so 1440/10.8 = 133 cars per day. If there are only 50 positions on the line then each car is 21.6 minutes behind the one in front of it or 67 cars per day.
At 133 cars per day, it takes 7.5 days to build 1,000.
At 67 cars per day, it obviously takes 15 days.
Now if I haven't totally bored you with math, I'll go back to an earlier post where I figured out that the plant could build about 83 cars per 24 hours. Using my trusty bamboo slide rule, I come up with a build time of about 17 minutes and a guestimate of 63 cars on the assembly line at one time... (Based on 18 hr build time per car).
Whew.. what kind of grade do I get for my story problem? My Solstice will be the one with the big gold star on the windshield.