Obvious acting. The black woman at 33:40 trying to simulate a level 3 possession deserves a 1.5 on IMDb. 
During a genuine exorcism, the demon(s) will rarely speak through the victim (one victim among many), that would be an extreme form of possession and a complete change of voice is exceptional. A one day exorcism lasts half an hour to 3 hours for deliverance. It can last a few minutes but only for unbaptized people.
If not within a day, it can take up to 3 months. The rest is uncommon and I am not talking about cases that are out of the Exorcist's reach.