970
xkcd #2846: Daylight Saving Choice
(imgs.xkcd.com)
Alt text:
I average out the spring and fall changes and just set my clocks 39 minutes ahead year-round.
They used to be used to note the change of the weather from one season to another, in a general range (not a literal single solstice date) sort of way.
However it does seem like the seasons are slipping in comparison to the calendar, Summer starting later and ending later, etc.