Hello Dan,
Thank you for your question about Bid Groups. Answers to your questions:
(1) To move a snipe to a Bid Group, you can the snipe again (without deleting the snipe) and specify the Bid Group.
(2) Bid Groups disappear after 21 days. You just stop using it. The 21 days is to cover any cases where you keep using the group over and over.
Thank you for taking the time to write in. Please let us know if you have any other questions. We are happy to help.
bidslammer