This year it was from April 5 to June 3rd, and next year April 3 to June 1st. One year it ended closer to June 10th and we got to go twice. We hit the last day of the festival, and got a bargain on the shirts!
In 2008 the dates are March 19th to June 1st. Even though Easter is quite early this year, they are starting it, I assume, so that the Easter crowds will be able to enjoy it.