If I have this:

SELECT SUM(DATEDIFF(d,Holiday.Start,Holiday.End))

...I can obtain 365.

Now, if I change the type to s, to obtain this same amount in seconds:

SELECT SUM(DATEDIFF(s,Holiday.Start,Holiday.End))

...I obtain 23533200.

However, If I do 23533200/84600, I do not obtain 365 days but only 272.38.

What am I missing?