Gets the estimated duration of this unit _in the ISO calendar system.
!(p)
All of the units _in this class have an estimated duration.
Days vary due to daylight saving time, while months have different lengths.
@return the estimated duration of this unit, not null
Gets the estimated duration of this unit _in the ISO calendar system. !(p) All of the units _in this class have an estimated duration. Days vary due to daylight saving time, while months have different lengths.
@return the estimated duration of this unit, not null