Last year we had a lot of new members, many of whom were asking about GB’s. So I posted this as a bit of a guide, hopefully that will help along with what then other guys have said.
cs.finescale.com/…/154045.aspx
As for the specifics on any GB, they will usually be posted with the first post of the build, the rules if you like.
Gb’s without a time frame or one that’s to long can sometimes just fade away, so as Johnny said, GB’s tend to run from between 6 months and a year.