A 2000 Chevy S10 does not have a timing belt.
Chain
The 2000 Chevy Trail Blazer doesn't have a timing belt.
The SC2 is an 'S' series Saturn, and all 4 cylinder engines of the S series Saturn's used a timing CHAIN rather than a timing belt.
The 4 cylinder Saturn engines used an "Oil bath" timing chain. The V6 Saturn engines used an "external" timing belt.
Change it every 100,000 miles.
That truck does not have a timing belt. It has a timing chain that will last the life of the engine.
It should be replaced when it begins making a noticeable noise.
According to the owners manual, for that vehicle the timing belt should be changed at 110,000 miles.
The timing belt should be replaced every 100,000 miles.
The oil pump is ran off the crank and is in the timing cover which requires removing the valve cover and timing cover. Not recommended for the novice mechanic.
90,000 miles or 10 years.