Laws of Cricket 1947 Code (Fourth Edition) - Law 11
The pitch shall not be completely covered during a match unless special regulations so provide; covers used to protect the bowlers’ run up shall not extend to a greater distance than 3 1/2 feet in front of the popping creases.
Note on Law 11
1. It is usual under this Law to protect the bowlers' run up, before and during a match both at night and, when necessary, during the day. The covers should be removed early each morning, if fine.
Reproduction of the Laws of Cricket is by kind permission of Marylebone Cricket Club