When will changing a major make you go to school for extra time?
This will vary depending on the school. Most schools have certain general education requirement courses (History, English, Math, etc.) which you will have to complete regardless of major. At a certain point you will have to complete prerequisite courses which are specific to your desired program. If you enter college as an undecided major, make sure you talk with a knowledgeable advisor and let them know your situation. They will be able to help you plan your coursework accordingly and assist in delaying your declaration of a major for as long as possible while still keeping you on track to graduate in 4 years.