Taking this more, my watch is always that "at" needs to be used for occasions that aren't days from the 7 days (at Xmas, at Easter, on the weekend, at lunchtime, at 9 o'clock) irrelevant of size, and "on" exactly where time is per day with the 7 days (on Saturday). I'd personally argue this is to do with The reality that "at" implies a particular f