If a car has sat for a while is it best to change the oil right away due to sludge buildup?

don't worry about the oil until you have checked and changed the timing belts, and pullys,that is, if its got them,the belt could be streached, and week, and all the pullys could be rusty, if they are, your belt will fail,in my expearence, oil is ok for years, and its cheaper than a cylinder head,hope this helps, but don't know what car, or year you are talking about.