A 12 cup coffee maker should brew 12 cups of coffee within 10 minutes.
If your 12 cup coffee maker is taking longer than 10 minutes to brew the 12 cups of coffee then it could have calcium deposits built up inside of it.
Sometimes the coffee makers spray ports where it sprays hot water into the coffee filter and coffee gets clogged with calcium deposits.
That can make the water not go through the coffee pot as fast as it should so it can make the coffee pot take a bit longer to brew the coffee.
You can clean coffee makers using some white vinegar or use some coffee maker cleaner.
Just fill the coffee pot with some straight vinegar and run it through a normal brew cycle and use a coffee filter.
Then run it through a few more times with water to clean the vinegar out of the coffee pot.
My 12 cup coffee maker makes the coffee within 10 minutes.