From May 1st and through May 14th anyone can leave Tok'ra related prompts on the official prompt post, which will be up in just over 1 week.
Claiming will open on May 15th and run through July 30th. The first two weeks each participant may only claim 2 prompts, to give everyone a chance to get their favourite prompts :) After that we open for additional claims.
Posting begins on July 31st and will remain open until August 14th. You can post at any time between those dates.
The requirement for your fic/artwork/podfic is only that one or more Tok'ra play an important part, and are not merely there as an easy way to get information and/or technology.
If you need them, the rules can be found here and the FAQ is here.