Ever since I appeared on television, the phone has been ringing every five minutes.
They came every five minutes until about 3.30, and then fizzled out.
Your contractions are probably occuring every five minutes or less and lasting at least one minute.
You don't necessarily need to buy two of everything when you are planning for twins, but you will want to stock up on extras so you don't have loads of laundry every five minutes.
For example, Cooks Illustrated usually sets the heat to 350 degrees and takes the temperature every five minutes or so to ensure consistent heating.