We always rest for 1 hour minimum and prefer 2 in the cooler. Warm cooler with hot water first. Vent heat from wrap before resting or it will continue cooking the the cooler and could over cook.
6 hours too long for ribs, depending on temp. Try 2 meat side up, 1 meat side down, foil for 1 hour, remove from foil, glaze and place back on cooker for 30 min to 1 hour. Check for tenderness with a toothpick into meat and pull when it slides in easily.
I generally cook at 250, but today I'm going to do 275 on 2 racks of spares and one slab baby backs. Testing a new rub.