ISODURATION function consumes a LONG duration in platform unit and pushes back a STRING reresenting an ISO 8601 duration. Whatever the platform time unit is, the representation maximum resolution is milliseconds.
The format of the ISO 8601 representation is
h as hours,
m as minutes,
s as seconds and
x as milliseconds. If any of these value is zero, the value and unit are omitted. The only exception is for a duration of 0 which is represented as
PT0S. If the duration is negative,
s, if displayed, are negative numbers.