Done correctly, it’ll take 24–48 hours. For best practices, suffocate your charcoal grill. Cutting off the air supply starves the fire of oxygen and sunsets any combustion. After closing off any airflow dampers and shutting the lid, give it plenty of time to cool naturally. Never add water to lit charcoal — wet charcoal is an angry thing, and it loves little more than to take its temper out on your grill’s metallic surfaces.