September 1st through 4th, inferred from:
How does the recruitment process work?
The recruitment process begins Tuesday August 31, with an orientation for those going through the process. The following 4 days are the times when you will actually be traveling to the different sorority chapter houses to meet the sorority women and learn about the different chapters. The first night when you travel to the different chapters houses, you will visit all 6 chapters, and be introduced to what they are all about. The following nights you will visit less and less houses until the final night when you will visit a maximum of 2 chapter houses. The narrowing down process is achieved both through your rankings of the chapters each night, as well as the chapters ranking of the girls they have met based on how well they feel they fit with their values. The process ends Sunday afternoon when bids are given out and you begin your new member period with your chapter house.
http://sites.lafayette.edu/panhel/recruitment/frequently-asked-questions/