Global bank, UK HQ.
Official policy is <=4hrs - Y, >4hrs - J.
Although this is down to your managers discretion. I have flown lhr to mex in Y and I know that senior managers have used private planes. I also know of cases when manager have only authorised certain routes as they are cheaper e.g. inconvient times and with connection so that both legs are <4, hence 2 Y flights instead of 1 J