Does a 2003 Buick century have a timing belt?
The first Google result says it all: https://repairpal.com/when-do-i-change-timing-belt-404
This car has a timing chain. No timing belt worries, then. Also, no chain worries according to the link. Some cars with timing chains have a chain system that isn't good for the entire life of the car, but apparently your car doesn't have such a poor timing chain system.