It is short for "Take 5 minutes", meaning take a short break. Usually said when people are working together in great concentration or effort, such as in a recording studio! A "take" is also a version of a performance as captured on tape, film, etc. used in the movie and recording industry. Often numerous "takes" are made until the assembly get it right, and each one is numbered, "Take 5" would be the 5th attempt. However, I don't think it means this here.