Around here, according to the prosecutor lady from the AG's office who teaches us all that search warrant-ish stuff, the exigent circumstances obtain from the moment the first responder gets to the scene until the last investigator goes home. That might be three minutes, three hours, or three days or three weeks. Once the scene is under the control of the investigating authority, it's THEIR scene, and Mr. Homeowner can sit on the lawn until the scene has been released.
Once the investigators depart, if they want to come back for a second look they need a warrant.
Mind you, the training I get is primarily for arson investigations, not homicides. But ... when responding to a fire, nobody can predict whether or not there will be bodies in the rubble, or evidence of arson. So ALL fire investigations are treated as potential arsons until arson has been ruled out.
