Determin period between two timestamps


I like to show the period between two timestaps

var DateTimeType StartTime = new DateTimeType() 
var Period wRunningTime = new Period(wStartTime, new DateTimeType())

But it seems that openHAB do not know the Period Type

any other ideas? The goal is to determin how long i.e. a washing machine was running. (in days, hours and minutes)


Probably some helpful stuff here