Nope, with some cars the next available spot in factory is months and months away. Try ordering a new Range Rover - standard wheel base model can now be ordered for the end of 2016, long wheel base you would get delivered around March 2017 if you ordered one now. Apparently that's because there's only one assembly line in their factory in Solihull, and there's thousands and thousands of orders from all over the world.

To be fair, waiting time for a new Qashqai(which is a very popular car) is still 3-4 months, because the factory is that busy.

Assembly lines require a huge investment and cannot scale beyond their maximum capacity. So when a car turns out to be popular, the OEM (the brand that does final assembly) or one of the many suppliers might run into a huge backlog.

That is most pronounced when orders spike after the introduction of a new model.

Why would a custom order need more capacity? Either a buy a standard model or I buy a custom model. The assembly line is basically the same, just a few different input parts. The assembly line will be rolling out the same number of cars per day. The difference being my custom order got sent to the factory and the next car started on the line was my car.

This has nothing to do with the colour and seats though. When "your" car finally rolls of the line to should take ... what? 1 working day to spray it the colour that you want and let the paint dry, an hour to bolt in your choice of seats and Cd/Mp3 player.

That is not how car production works. Paint is literally the second thing that occurs after a chassis and body panels are applied. But otherwise, the working time on a car from start to finish, including paint, is somewhere in the 10-20 hour range. Theoretically, your timeline could work but paint takes time to cure, then needs polish and interior features take a while, although CAN-BUS has certainly made the electronics easier.

And nobody claimed otherwise. Order backlogs introduce the large delays; manufacturing/shipping takes days or at most two weeks.

They're much faster than that. Individual cars are produced in under 24 hours time wise across pretty much every major manufacturer.

There are other reasons than just manufacturing time, for why a vehicle would take weeks or months to get.

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.

If you start with a few stock models, and then all you're picking is the colour of the paint and the style of the seats and a few other bolt-on parts; then no, it should not really take long.

I think distribution would be a big factor here as well. Ideally manufacturers would like to batch shipping as well, which may require some minimum number of orders from a particular area for a particular type of car.