FuzzyCo

Isn't it after 90 days of being posted or something like that?

Well, yes, here's the relevant section from their submission terms (last revised July 20, 2007):

"In addition, by submitting your Design, you may not reproduce, sell, or submit the Design to others for any commercial purpose for ninety (90) days after the date of submission while the Design is being evaluated by Threadless.com. Once the ninety (90) days have passed, if your Design is not chosen for print by Threadless.com, you are free to use the Design for any commercial or non-commercial purpose. However if your Design is used elsewhere, you must notify Threadless.com by email art@threadless.com about where and when the Design will be used, so that it can be removed from the Threadless.com website at that time. In addition, if the Design is used or reproduced for commercial purposes elsewhere, you cannot use the Threadless.com blogs to promote the Design or the company using the Design."

That all seems very reasonable to me. From their FAQ:

"How are the winning submissions chosen?
We look at the top 300 designs every couple of weeks and pick out around 10 designs that we want to print based off of the designs score, comments, and the number of i'd buy it's. Ultimately the decision of which shirts get printed are left up to us. The scoring system helps give us a general idea of which designs our customers want." (emphasis added)

Basically, they want 90 days to make a decision.