In the new system, you must join or create a co-op in order to start progress on your Contract farm. When creating a co-op, you may choose to start it at any time. You may wish to let the other slots fill up with people first so that everyone gets the full amount of time or you may wish to start immediately. The lobby system is known to be fairly buggy, with some players receiving a "full coop error" even though the coop has open spots.