Generally when I start to ai the heifers I watch before hand record dates so I know when there on again, have cameras in the shed and be checking them haven't missed a standing heat in a while, and by late if I seen a heifer standing this morning at 8or9am I would bull her the following morning before milking. Suits me as I can do it, not everyone would want to due to time constraints or labour. But I would be getting 80-90% first conception to sexed. Only working with batches of 10-15 heifersHow do you define late as possible? Your never going to know when the first standing heat was or when the oestrus cycle first begun??