There is no fixed date for it ; it usually takes place in the middle of the week late at night, once the initial explosion of the first days has been got over.
It started some thirty years ago and the idea is that a crowd collects behind the Town Hall with any kind of musical instrument or anything that can make a loud noise, and they set off on parade through the streets.
Anybody can join in, grap a drum, or whatever and get down there to the Town Hall about 12.00 midnight. At this hour they always play the traditional piece _ Agur Jaunak, and then set off round the nearby streets. They always finish three or four hours later at the little well of San Saturnino, half dead and half sloshed (from the many stops for refreshment made along the way).