In Sweden it is majority of parliament, election, then majority of parliament. If a motion to hold a referendum is presented in the first parliament it takes 2/3 in the first parliament to stop it or a referendum with veto-powers (only a no is binding) would be held at the same time as the election.

In real terms the election of 2014 is the shortest time, but theoretically I guess an extraordinary election would do in Sweden (I am not certain). If an extraordinary election does the trick, then an election can be called three months after the decision, but it still has to pass nine months between the decisions, unless you can muster 5/6 of the first parliament to say otherwise. So with 5/6 in the first parliament and majority in the second, the constitution can be changed in 3 months. Probably.

A vote for PES is a vote for EPP! A vote for EPP is a vote for PES! Support the coalition, vote EPP-PES in 2009!