Wait for no longer than 10 minutes when you are dealing with an emergency situation. Service providers should be there within eight minutes in optimal circumstances. The eight-minute window is the time when receiving medical services is the most critical for patient survival.If you are waiting for an ambulance and it has not arrived after 10 minutes, call 911. Let them know you are still waiting for emergency transportation and the ambulance has not shown up.There could always be an accident or other situation where the ambulance is unable to arrive on time. You also need to request an additional ambulance in this instance. Therefore, call 911 when you are waiting for a late ambulance to arrive in an emergency situation.