I'm not asking about the length of daylight for the winter solstice. I'm asking about whole days that are shorter than 24 hours. For example, anywhere that observes Daylight Saving Time has one day each year that is 23 hours long. Any location that decides to change time zones can also experience a longer or shorter day, that day. Given all such factors, where and when was the shortest day? You can ignore days that were skipped entirely.
PS: I'd love to know the longest day, too.
EDIT: Imagine a person with a desktop calendar, one page per day. Every "day" he flips one page of his calendar, or more pages at once if he is changing calendar systems. I want to know how close together two such separate flipping events would have occurred.