I know the "flushing" concept applies with humans. Don't see why it wouldn't with the birds. Sometimes we wait, sometimes not. It only matters here if we want to be 100% certain of the father and would have trouble distinguishing from the chicks. Like if the fathers are the same breed and variety. Same with separating eggs into different baskets for hatching if we want to keep straight on the mother. Depends on what your doing and how good of records you need or want to keep.