Sarah,
My understanding is this is an open email list to post jobs within the realm of PostgreSQL. As such, there is 0-cost--as it is to support the hardworking community of PostgreSQL DBAs and Programmers--and length of time is both immediate and indefinite. By this i mean, once posted here it will be pushed out to all subscribers of this mailing list--or aggregated and sent out at EOD if the user has selected digest. Once submitted to the mailing list it will end up in the PostgreSQL archive which is Google indexed and is provided for posterity.
I have included a link to the message archive for this month, here you may see some of the examples others have put out.