There was a warning (NOTAM A3308 from memory) issued at @13:00 that day - but not only did it not give the possible delays incurred, only traffic restrictions MAY be applied, but it also did not seem to arrive at many units!. .Even the flow message at 20:30 did not tell us that massive restrictions were to start at 21:00..... .Seems the biggest lesson to be learnt is to tell the users whats going on in advance and let us plan around it.