As the various links explain (and you should read JohnZs assembly process report also), you can use this data and the math with approximations to get kinda/sorta about when a car was built. But it isn't guaranteed to be exact, as we disclaim all over the place. The only way to know for sure exactly when a car actually came of the assembly line is to have a piece of GM paper that says that, and those are rare.
LOS cars have a Fisher production date code that gets you an idea of the working day of the month when it got tagged on the Fisher side. GMAC papers have the shipping date that is usually within a day or two, no more than a week, later than production. BBCs have the order rec'd at factory date that also tends to get you close. The Manufacturer's Statement of Origin has the transfer date from GM to the dealer that is no later than the shipping date.
I was fortunate to find the MSO during my extensive title search for my car, a 9Jan68 MSO date for my 01B car that is LOS with a J day of month in the scheduling code, which is interesting - our other data show that the January scheduling period started during the 12E week and accounts for a couple of days - and taking other things into account, the J day from our other data has to pretty near be either the 8th or at most the 9th for my car, meaning that it would have been built and shipped very fast, which isn't always the case. And that also means they did something wacky with that first A week of the year, which they do seem to have done (perhaps like spending more of that first short week building Impalas rather than Camaros). That these dates don't fit a conventional calendar is one of our points, and unless you have several pieces of converging data, getting closer than a week is pretty uncertain.
However, our Canadian friends are fortunate in this regard as the GM Canada data has both the build and ship dates included.