Total number of seconds represented by the datetime quantity.

Currently, the datetime quantity must be of the form ddddThh:mm:ss, where dddd is four digits for the number of days to add or subtract, hh is two digits for the number of hours, and mm and ss are for minutes and seconds.

You can make the quantity negative by putting a minus sign in the front. If you do, you will get back a negative number of seconds.

We may, in a future release, allow changing the format of the datetime quantity.