Sequencing activities in a warehouse based on when it is going out the door makes a lot of sense…in theory.  In practice, ship times are often clustered around the beginning and end of day shift, meaning that it is necessary to pick hours ahead of the scheduled ship time.  JIT inventory practices create inventory availability miss matches, so workers go into the racks to pick orders for which all the inventory is not yet present.  Later, closer to shipping time,  they go back to get the missing product.  Effort duplication = stupid.