After a week of trying this or that I think I found a way.
def today = timeToday(null, location.timeZone)
use (groovy.time.TimeCategory)
{
newDate1 = today+3.hours
}
logMsg "New Date: " + newDate1
Not sure if using use (groovy.time.TimeCategory) several times in an app will cause issue, or is there a way to import it in the header.