You can have a beer carbed in 2 hours if you want to. Get it really cold, crank the psi and shake it. It will be carbed in hours.
However, it will still take about 3 weeks for the carbonic acid levels to equalize and the beer to stabilize to a normal condition. You can serve your beer after a fast carb (I have) but it will not be as good as it can be and will be in 3 weeks.
Now, realistically, how many people will sense that something is weird about your beer because of funny carb or higher than normal carbinic acid levels??? not many.
As with everything homebrew, there are tons of ways to do it, tons of opinions, and tons of corners that can be easily cut if you don't really care that much.