If your car is a 3.1, it doesn't have a timing belt, if it's a 3.4 DOHC, it has one, but it has nothing to do with the water pump. Changing the water pump on these engines is a 45min job (removing serp belt and 9 total bolts). Make sure you bleed the air out of the system afterwards. That can be more difficult and time consuming than actually changing the pump.