Oops
Sorry David
I misread your question about "How long between the elections for Prime Minister?"
I thought you were asking when we were going to vote for PM (Prime Minister).
Oilgun set you straight on that one, however ...
Only recently (Harper did this) has the rule of 4 years maximum between election been in place. Often, past majority government did stretch the 4 years out to 5 years. And even once, during war time, elections were suspended all together.
Minority governments are not expected to last 4 years. In this case, Harper called the election before the 4 years had lapsed. Usually early election, during a minority government, occurs because the opposition loses confidence in the ruling party and votes to defeat it. Harper felt he had a chance to produce a majority government so he called this one. Course he messed up and we're still in pretty much the same minority government situation as 6 weeks ago ... except now he doesn't have to call another election for 4 more years - unless, of course, he gets defeated in the interim.