til the cows come home

(un)til the cows come home

Rur. until the last; until very late. (Referring to the end of the day, when the cows come home to be fed and milked.) We were having so much fun that we decided to stay at the party until the cows camehome. Where've you been? Who said you could stay out till the cows come home?
See also: come, cow, home, til