until the cows come home

Until the cows come home is a very common idiom used when referring to something which will not happen for a very long time, usually an indefinite amount of time. IT is most often said in response to someone asking when a certain event might occur, and the answer will be not until the cows come home. When cows leave home, or escape from where they live, they dont normally find their way back home which is where the phrase originates from.