Originally Posted by
blackbox
Quarterly yes. But, where in that quarter? The beginning? Middle? End? Again, basically at the discretion of the company to produce the list four times a year. They could produce it January 31st and then again on February 1st. (If it's the fiscal year.) Or March 31st and April 1st if you're looking at the calendar year.
The last three updates are dated 12/23/11, 3/9/12, and 6/1/12, so it looks like they're sticking pretty close to the beginning of each quarter.