Yes timing belt is partly wear and tear item. Why i am saying partly because you suppose to change it before it wears down
Snapping or tearing of timing belt can cause BIOG HAVOC to car engine. So stitch in time save nine.
After 100k km you should change the timing belt in Lexus (not sure abt SC though). But quite positive as its same in all Toyota and Lexus models. Still double check with dealer the exact km to be 100% sure