It is probably not a belt, but rather a chain
When I bought my '02 I was told that it no longer has the timing belt/chain that needs to be replaced at around 60,000 miles (my '96 did have a timing belt that needed to be replaced every 60,000 miles). I have put over 80,000 mi. on my '02 and nice to know I won't be getting surprised by timing belt failure. Did have to have the serpentine belt on the engine replaced recently though.
It does not have a timing belt it has a chain
The timing chain should last the lifetime of the engine. I would like to know the symptoms.
No, You do not need to remove the oil pan to replace the timing chain. I don't know why you think the timing chain needs replaced. But I would make Darn sure that it does before you tear it down and do all that work for nothing. The timing chains on todays engine normally will out last the engine.
You don't, that's why timing belts and chains are replaced with certain mileage intervals regardless.
If it is equipped with the 2.0 liter 4 cylinder it has a belt that must be replaced at 60,000 miles. All other engines have a chain.
The timing chain has no regularly scheduled time or mileage for replacement. It will normally last the life of the engine. They are routinely replaced when a complete overhaul is done. You will know if it needs service. It will become noisy, and your engine may not run correctly if it jumps a tooth.
The Pontiac Grand Prix has a Timing Chain with a spring loaded tensioner. The tensioner is know to wear, crack and then break. The timing chain and tensioner should be replaced at 100,000 miles. This is a pretty big job that can be done with the motor in the car. $$$ Ray
With some engines this is necessary. See the manufacturers recomendations In all cars I know of the timing chain will last the live of the engine under normal circumstances. It is replaced during a complete engine rebuild.
It needs replacing every 60,000 miles.
Take the dist cap off and watch the rotor. Turn the engine back and forth and see how much the engine turns without turning the rotor. If you move the balancer more than about 3/4 inch, I would say the chain needs replaced.