Crib time Definition
Crib time is the expression generally used to denote a paid meal break prescribed for employees on certain types of shift work or for those employees working overtime. In most cases these breaks are of a shorter duration than unpaid meal breaks generally allowed to employees, the usual practice being to limit them to periods of 20 minutes. Some awards may provide a 20-minute paid crib break to an employee before starting overtime work after ordinary hours where such overtime is expected to exceed (say) 1½ hours. Where an industrial instrument prescribes that a crib break is allowed after a period of overtime ‘without deduction of pay’, this means the employee receives payment for the crib time at the appropriate overtime penalty rate. See re Tramways (Melbourne) Award (1959) 92 CAR 387.

Edit futher digging says it is of cornish mines origin Crib - a mid-morning break for a snack, maybe when Cornish pasties were pulled out?
The Oxford English Dictionary (2nd ed.) has "Food, provisions, light meal, etc." (dialectal) as one of the meanings of "crib" giving several examples including quotations from M. A. Courtney's Glossary (1880) and Rowse's Cornish Childhood (1942).