They can take a while when they are in a house, they don't necessarily just scoop and run, sometimes they may treat someone at home to avoid taking them to hospital, or perhaps the person doesn't need the hospital but they need to see a doctor out of hours (and the ambulance may wait whilst they are waiting for the doctor... if they are going to someone who is violent they may need to wait for the police to come... there are tons of reasons that an ambulance may appear to be just sitting there for ages.