A string of the form ddddThh:mm:ss, which contains number of days, hours, minutes, and seconds the seconds converts into.

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 pass in a negative number of seconds. If you do, the datetime quantity returned will be prefixed by a minus sign.

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