Remember that pineapple is a natural meat tenderizer. Fresh juice has much more of the active enzymes and can over-tenderize meat if left too long. A whole big roast will be fine marinating overnight, but small pieces of meat will disintegrate in that time. Four hours is enough. Using canned or jarred (pasteurized) juice, you needn’t worry about over- marinating.
Find it online: https://hilahcooking.com/how-to-make-tacos-al-pastor/