What is the difference between "I remember the day where..." and "I remember the day when..."?
I think both are used in both written and spoken English. Can we say that "when" makes more sense when we are talking about a specific point in time?
As the other answerers suggested, the day when seems to be very common. In most cases both the day when and the day where refer to time, not place; but the day where is a bit archaic.
In my research, the only instance I found in which the day where refers to a place – not time – is in the book The London Encyclopedia: or, Universal Dictionary of Science, Art, Literature, and Practical Mechanics. VOL. X. 1893:
That said, it seems that other authors have used it by referring to a time not place. Here are just a few examples:
The King James Bible (Job, 3:3) has this: ‘Let the day perish wherein I was born, and the night in which it was said, There is a man child conceived.’ However, the day when is almost certainly what would be used on most occasions now. Do you have an authentic quotation showing where in such a context?
I remember the place where...
I remember the day when...
I remember the day that...
is also possible because some people argue that the combination "day" and "when" is redundant.