Getting this further, my check out is that "at" ought to be used for situations that are not times of your 7 days (at Xmas, at Easter, with the weekend, at lunchtime, at 9 o'clock) irrelevant of duration, and "on" the place enough time is a day on the 7 days (on Saturday). I would argue this is to try and do with The truth that "at" indicates a spe